Huh?
Just start at the morning and think yourself through the day, note everything you'll be using.
Maybe it's a bit chilly at first, so you might want some warm riding clothes. Then both you and the day warms up, so you want to shed a layer. You'll need something to drink soon. Means water bottles + holders. Then you'll get hungry. If you're passing through towns there are restaurants and shops. If you're out in the middle of nowhere you need to carry food. Fancy a hot meal? Then you need a camping stove, fuel, cutlery and a plate/bowl. More water. Ride on. Plan to continue into the evening? Then you need lights, reflectors, and I'd strongly recommend Hi-Viz vests.
Or you stop and make camp before it gets dark. Where? Middle of nowhere? Campsite? You'll need lamps to get around a bit, probably another meal. Maybe want to freshen up a bit, if there's water. Soap, shampoo, towel, toothbrush etc. Give your riding shorts a rinse. Then it's night. Sleeping bag, camping mattress, tent.
Then it's morning. Another meal. Pack everything up. Mount up, ride on. Maybe one of you have a flat. Roadside fixes are unpleasant. Carry a spare tire and the associated tools. Put spare in, get outta there. Patch tire while your buddy prepares lunch later in the day. You'll probably want to carry some more tools and spares to avoid getting stranded. Chain breaker, some quick links. New brake pads if you run rim brakes. A length of duct tape. Tools to adjust saddles and handlebars.
Weather can turn nasty, carry some water proof clothes.
One of you goes off the road. Nothing serious, but you'll need to clean & cover those cuts and scrapes. Carry a 1st aid kit, boost it with some band aids and stuff for the minor injuries too.
Weather can turn too nice, you fry in the sun. Stuck in the same position, heading the same way doesn't help. Carry sunblock.
Now, this is a kind a generalized plan. If you're in a place with real reliable weather, maybe rain gear isn't needed. Maybe you can use a blanket instead of a sleeping bag. Or maybe you can use sleeping bags instead of a tent. Maybe you're not going that far, and there's someone who can act as backup, drive out and get you. Then you don't need to carry as much parts and tools.
Do note that there's an art to enjoyable bike camping. There's a limit to how much you can carry on your bike. If you're going for full tent, sleeping bags and such, front and rear panniers will help a lot. Sticking it all on a rear rack will stress the rear wheel bad and generally make the bike a bit unpleasant.
Riding with a backpack is possible, but to be able to enjoy it, you really need to travel light. I'd say 20 lbs before it begins to get real uncomfortable for longer rides.