I use to live in Bakersfield too, and Action Sports is a fantastic bike shop and the guys there can really be a big help with preparing you for that ride. 58 is a dangerous road to ride alone, you would be better off in a group ride along that route, but it's the only route to SLO without a long round about way. Kerry Ryan use to be the owner there when I lived there and I think he still is, is a very nice man and will gladly speak with you if he's in.
I rode from Bakersfield to Santa Barbara and I took 3 24oz Polar bottles on the bike, a 16oz in a handlebar bag, PLUS a 70oz Camelbak and still needed to get liquids and food at Ventucopa and again at Meiners Oak or Mira Monte (their almost the same town). The problem with your ride too is that your coming from SLO meaning your leaving in the cool of the coastal morning and arriving in Bakersfield in the heat of the evening desert, and depending on what time of the year you leave you could be riding in 90F degree plus heat for much of the ride. I left Bakersfield at 5:30am so I could get across the desert floor and into the mountains before it got too hot then arrived around 4:30pm in Santa Barbara but it was cool there which kind of refreshes you to finish the ride.
Make sure you take at least a dozen patches and your glue is new...you don't want surprises with a dried glue tube, and a tire boot patch kit. Get a set of really good puncture resistant tires because once you come down into the desert goatheads will be hunting for your tires and lightweight racing tires won't stop them!! Carry at least one spare tube and carry a spare tire just in case you destroy a tire it's rare but it does happen and you don't want to be stuck in the middle of nowhere without a tire. And don't forget a mini tool. When I did my trip I carried a frame pump PLUS a mini pump just in case one pump broke.
I would also run with a bright flashing red tail light like the Blackburn Mars 4 or whatever you have on 58 just to make sure folks can see you. Take a light rain jacket just in case and store in a handle bar bag. If you have a front light I would take one just in case you run into a problem and you end up riding when it's getting dark.
Here's some images of goatheads, the thorns are in multiple positions and no matter how they lie at least one thorn is pointing up, they also turn brown when their old and are still just as bad. These things once penetrated my foot to the bone! That hurt!
http://www.bing.com/images/search?q=goatheads&view=detail&id=86DFD31770AEA6205435F3A56CC4F84A30F4932D&first=0&FORM=IDFRIR