I know everyone mentioned it already but you really can't bring too much water. I biked last year from Albuquerque to a camping spot 20+ miles off the "main" road somewhat near San Yisidro, New Mexico. I was going to meet friends there and was using the trip as a tester trip for a longer tour that summer. I have never thought more about water in my life. I brought about 130oz (approximately six water bottles for a 75 mile trip). I had to conserve from about hour one on. If I were to do it again, I'd bring twice that amount of water-- 250oz a day. When you're out there, nothing else really matters. I carry these Nalgene collapsable water containers that fit about 100oz and put one in each front pannier. I refill the water bottles from them and it is a nice way of scheduling breaks-- forces me to get off the bike and walk around a minute.

Something nobody mentioned. Don't bring anything that's going to melt-- food stuff, candy bars. Learn from me!-- It's just a huge mess!

Chuckie