there is a lot of good advice above, but i couldn't resist adding my 2 cents.
i rode out to san francisco on the valk last summer (from dallas). outbound, we took the route into hobbs, nm, thence to carlsbad, then north to artesia, then west over the mountain at cloudcroft and down into alamogordo then dropped back down to i-10 at las cruces. if you have time to do it, this is entirely worth it!!! you'll be frakkin' done with flat, hot, west texas plains by the time you make abilene and this affords you a lovely (and cool) detour. on the way home, we came through nevada, utah, colorado, and into new mexico via raton pass on i-25, through dalhart to amarillo and back into dallas on US 287.
also, i-10 through tucson is under VERY NASTY construction right now. i was there for work in february and it's worse than it was last summer. you can get off i-10 between Las Cruces and Tucson at Lordsburg and onto the old US highway 70 route which will cut out both time and distance and spit you out right in phoenix. unless you absolutely must stop in tucson, you're better off taking this shortcut.
gear-wise, i found a cooldanna was surprisingly helpful, as was my camelback. i put ice and a mixture of gatorade and water into it at every gas stop and then i kept my eye drops in the backpack with the bladder. that kept the drops from being sahara hot when i used them. i soaked the cooldanna in the ice bucket in my hotel room every night and wetted it at gas stops, it stayed damp all day long. when i'm on summer trips like that, i wear summer weight military issue (not wal-mart!) camo pants because they stay drier and cooler than jeans and have pockets large enough to store an entire trauma team. we needed long sleeves and warm gloves when we crossed the continental divide in colorado on the way home, and our long sleeves and rain gear (for wind-breaking) in san francisco and other parts of northern california. i also found some jogger's wicking underwear at academy that was a godsend when crossing the deserts.
don't forget to use sunscreen on your exposed parts. i had an utterly regrettable day in california on which i only put sunscreen on one of my arms. i think i got distracted by a motorcycle...
bike-wise, i had a compact tool set, bungee net, zip ties, ziploc baggies, shop towel, small can of plexus, kickstand coaster, jumper cables, compact first-aid kit, flashlight w/ batteries!, tire plug kit, spare cloth for covering the seat on sunny lunch stops, spare fuses, electrical tape, duct tape (flat pack!), tank bag for keeping camera/ipod/snacks/chapstick handy, a book in case i got stranded somewhere, an extra oil filter isn't a bad idea (although i forgot to take one). also, an umbrella is great to carry, in case you get stranded in a place with no shade or in the rain.
hope this helps! i wrote up most of the trip on my blog if you care to see details about the route or our stops:
http://thalashouse.blogspot.com/search/label/roadtrip07
