For your body, don't try to stay dry--just pre-plan to dry instantly:
Silk, Nylon, Polyester, Vinyl, Rayon. . .
These usually dry in 5 minutes or less, unless they're padded or fuzzy.
Also helpful is not to wear any underwear.
It self-destructs when cycling anyway.
However, I'm certain that Nylon, Silk, and Polyester underwear is available for both genders, and this does not have the awful sensation of soaked cotton or wool.
Un-padded bike shorts upon a padded saddle make a nicely waterproof combination. The white color is extremely embarrassing when it gets wet and thus transparent.
Ordinary Mountain bike shorts are all bombproof and most of these dry quickly.
Waterproof materials from backpacking/running sports provide what you need for longer pants.
For commuting to work, polyester or polyester blend dries out the very second you sit on that nice dry towl you keep at the office.
In a muddy emergency, carry the dry towel to the restroom, wash the pants in the sink, wrap the pants into the towel, step on the towel and then put on the clean, dry pants. You can also just keep an extra set of clothes at work.
Nylon men's "dress" socks are nearly impossible to get wet. They do not absorb water at all.
Similar socks are available as sport-centric backpack/running socks, and those can be comfortably thicker, and some have the nifty trick of holding the water away from your feet.
Extremely cheap all-manmade shoes with as little padding as possible will dry in 5 minutes flat--if you stop at the nearest restroom and cram (CRAM!!) them full of paper towels.
Newspaper also works, but it may print your hands.
Wait five minutes, yank the paper out and you're dry.
With manmade clothing materials, it is only necessary to shake the water out. Loose weaves get rid of water faster than tight weaves.
Remember to wear at least two layers of manmade materials if you are exposed to "cold" rain.
You may also want to pack spare towel, socks and T-shirt into a plastic bag in your panniers. No panniers? That's okay! A "frame pack" or a "trunk bag" is much more areo, so use one of those instead.
Fenders or not, your face will get covered with road-stuff, so do wear some bike or motorcycle eye protection.
For CARS, and avoiding them:
Know that a bike is impossible to see in the rain and so is a steady front bike headlight.
However, it is possible to mount a pair of lightweight 2xAAA battery powered white flashing lights (looks like the rear blinkie) and get them as far apart as possible. Serfas makes some painfully bright 3xAAA 5-led featherweight blinking headlights that just clip right on with a nifty adjustable clip. Installed "normally" they are quite waterproof.
Your headlight is normally pointed down, making it unnoticable. Point your indicator lights 1 into where a car driver's face would be and 1 into where a truck driver's face would be. Note, that you should never use blinking lights on the sides of the bike because car drivers will mistake these for turn signals and assume your direction is indicated.
For the BIKE, the following materials are helpful:
"EPIC" chain lube for dirty conditions (chain, exposed cables, moving parts that don't have grease).
Also, safe for use on Carbon Fiber bikes.
Singer Sewing Machine oil for road racing (chain, exposed cables):
It, plus a paper towel, can also clean horrible stuff out of your chain, and comes in tubes small enough to fit into an under-seat flat-pack. Recently, on a 480 mile tour, I used this once on my bike and several times on others bikes. They had used marketing based $20 "Teflon Super-Speedy" (I made that name up) chain lube. Their drivetrains started to jam full of road grit. One, surprisingly strong lady, had used "White Lightening" origional formula that does not penetrate the insides of chains (neither does most non-clear chain lube). She had been complaining of terrible shifting problems, occaisional walking up hills, and thought her Sora crankset had bent chainrings. Of course it did (they're steel), but it wasn't bent out of "normal range" for that system. After a quick check to make sure her bottom bracket didn't rock, I gave the chain a dose of Singer oil. The inferior lube came off in gobs, leaving the chain clean. No derailleur adjustment was necessary because it had just been to the mechanic for shifting problems. I was headed up the same hill as she, at a nice 14mph clip (for a mountain foothill), when she passed me like a strong breeze. This is not surprising considering that it increases the speed of sewing machines by nearly 400%.
Science works on metals, marketing does not.
Caution: Fully Carbon Fiber bike frames should be cleaned with mild dish soap (like Palmolive origional formula), rinsed, and then waxed (grit-free wax) after any exposure to petroleum products or. . . anything. Suggestion: Use this oil once per new chain and twice per year (gets inside the chain), wash bike, wax bike, and then switch to EPIC chain lube (or any clear bike lube) for regular use.
Aluminum bikes are un-affected by light oils, and it is highly beneficial to steel bikes (of course).
Caution: Petroleum products should never touch tires. Use a bit of cardboard between chain and tire when applying. Wipe chain throughly with a cloth to remove excess. Got a spill on the tire? Dish soap, rinse, vinyl shine spray (Formula 2001, Armorall).
Caution: This oil is intended to protect bushings and sliding parts made from nylon, aluminum and steel; however, it is not suitable for ball bearings, so keep it away from headsets, hubs, and bottom brackets so it doesn't clean the grease out of them.
Automotive wheel bearing grease (sealant for the water-entry points on headsets, hubs, bottom brackets)
If your rear-derailleur's sprockets don't spin right, you can combine with oil or EPIC for the insides of rear derailleur sprockets, using oil or EPIC on the bushing and grease to seal it in there).
Good quality car wax that is grit-free (clear-coat wax).
Champagne/wine corks can be jammed into old style seatposts or into the often-exposed area between the top of the front wheel and the forks. The corks may be greased to make them completely waterproof.
"Blue Magic" automotive aluminum wheel wax prevents corrosion for 6 months after application to any exposed metal.
Simple Green cleaner or dishwashing liquid (soak the already-soaked bike and put it in the shower).
Note: A too-high concentration of this will strip the waxes off.
Note: Any form of soap damages rubber; however, this damage can be stopped before it starts if you spray the bike with Vinyl protectant (Formula 2001, Armorall) as soon as the bike is dry. Skip the saddle, flood the tires.
Vinyl protectant can also temporarily substitute for waxes that got removed by accident--an easy way to preserve the bike in-between waxing. Please don't allow any of this to dry onto the saddle; however, it may be applied and then immediately scrubbed off with a towel in case of accidental exposure of the saddle to degreaser.
Note: Re-oiling the chain and inspecting other parts that should stay lubricated is necessary every time the bike is washed.
Note: Please don't spray de-greaser into hubs, headsets, and bottom brackets. They're supposed to be greasy.
Car wash? The car wash will destroy headsets, bottom brackets, internally geared hubs, any rear hubs, and front hubs. Specialty mountain bike products are no exception.
All the little rusty screws? Well, if they hadn't previously been packed in Blue Magic aluminum wheel wax, they are now rusty. Get an extremely cheap can of weatherproof silver (aluminum color) spray paint--and a small package of childrens watercolor brushes. That kind of paint has rustproof aluminum in it that causes the shiny silver color. Since the screws are rusty, there was no protectant, so it requires no preparation. Spray paint onto the little brushes and dobb the rusty screws. No problem. However, if you are obsessive, rust neutralizer, such as Naval Jelly, can be used as preparation before painting the rusty screws (follow directions on the rust neutralizer).
Do please run treaded tires so that you can stop in the rain. Yes, I know that tread does not help cornering. Yes, it is true that there is no possibility of hydroplaning a bike (unless "colored" non-carbonized rubber touches the road, and that does hydroplane).
I also know that there's no possibility of safely stopping a bald tire on a rainy city street IF you repeat this test several hundred times. Treaded tires stop in the rain. It doesn't take much tread, and it must be on the contact patch. It has a sandpaper effect upon the road. Bald tires have an "ice skate" effect upon the road.
Racing application:
If the idea of Panaracer's speedy ZSG rubber compound found on T-Serv treaded tires (small sizes can race--well and you always receive one size even smaller than you intend) is objectionable, and you have NO need to STOP in the rain (you just want to make it around the corners), then the new crop of dual compound/tri compound racing tires is what you need. Please avoid all colors except for black and gray (all-black is reportedly safest).
In fact, if one wheel is more "slippery" than the other, just put the T-serv on the slippery one and a matching top-of-the line ZSG racing tire on the other.
When you're not going to crash, racing in the rain is great fun!! I just love the rainy summer racing where it isn't cold and it is impossible to get hot.
Leather saddle? You can apply proofhide to the top and bottom. One day later, you can apply mink English horse-saddle specific dressing. Minks are waterproof, and the use of this product does not increase the number of minks that are harmed for their fur.
While the Raliegh/Diamondback Avenir saddles are far more comfortable in almost every way, they're not as "air-conditioned" cool as the leather saddles. Still, the Avenir requires no special waterproofing, and they are available in the rare combination of touring width plus no springs if you wish for a lightweight, very comfortable and maintenance-free alternative. Note that if you switch from leather to a medium or wide Avenir, you may want bike shorts with no padding. And that's exactly what you want in the rain. No padding in your shorts=no water in your shorts.
P.S.
Still like the idea of rain gear? Okay. Well, it is very nice for your shoes. Small bits of elastic can be attached or tied to rain gear. Rain gear made for running sports works very well without all of the excess heat.
P.P.S.
Front fender can keep a small amount of water out of your face. The lightweight plastic fender will do just as good of a job as a heavy fender.
There is a better option for a rear fender:
For the road bikes, a lightweight clamp-on rear rack that has the solid stripe of aluminum down the middle keeps the water off of your back, and can also tow a "trunk bag" in your draft without slowing you down, since it is directly behind your butt. This is a great place to keep the dry towel, lightweight dry shoes, or to ditch the rain gear when the sun comes out (and you get the sunblock out of the trunk bag).
City bikes can use the inexpensive Sun-Lite rack that bolts in place and has that same solid aluminum stripe down the middle. By using the 700c model on a 26" wheeled bike, it is still possible to elevate a trunk bag up into your draft for areo advantage and easier pedaling at speeds--this is not a good idea for a heavy load because of balance, but works well for a light load without cutting speed. Be sure to get a short "graded" bolt in the correct size for the right-side lower rack mount so that a nut doesn't block your chain.
P.P.P.S. Scotchgard doesn't work at all for waterproofing, but camping/hunting sport specific fabric waterproofing spray works just fine.
This has all been "in my opinion." Also, "in my opinion," you should not believe me or anyone else--find the truth for yourself. Why? It is often highly application-reliant.
Although I wish you would believe me when I say that there are a limited number of street/road treaded tires available that are just as fast or faster than bald/slick/racing tires, and that the mildly treaded tires usually add the feature of stopping in the rain.