WOW! Thanks everybody!

I am really enjoying all of the responses to my question. Great information. Thanks for taking the time. A lot of great tips for riding in hot weather.

I would like to add one thing that has not been mentioned. ICE. You know...frozen water that comes in little pieces. I have a Polar Bottle that keeps water cool for about an hour if I fill it with ice cubes, then add water. Way long enough for commuting + errands. Drink it or squirt it through helmet vents (if you wear one) for head cooling. Works great.