Everyone has offered good ideas. In Phoenix, it's not always a dry heat, and anyway, hot is hot. I use the Camelbak for water, and on long rides, carry an extra bottle of water plus a bottle of Gatorade with lots of ice. As the ice melts, it brings the Gatorade to a solution my stomach can tolerate in the heat.

The thing about heat is to acclimatize gradually, if possible. Give your body a couple weeks to adjust to the hot weather. As a teacher, I have duties everyday that require me to be outside quite a bit, so that my adjustment happens naturally. I guess people who work indoors all the time would have to force themselves out into the heat to get their bodies to adapt. However, I have to admit that you can only acclimatize so much. You have to respect the heat and the sun: they can be deadly! Even when I was in really good condition, I still had days where my body just fizzled. In Phoenix, we know we just have to go slower and go shorter--and that that is just as good a workout as longer and farther when the weather is cool.

The main thing is to be patient in the meantime, and try not to push it. Too much too soon in the heat=BONK. Bonk=misery. So ride early in the day, and don't be afraid to call it a day if your body can't take it. There will be other days.

Enjoy your rides! Have fun! Then hit the A/C!