Thanks for the great suggestions, they're all very practical and easy to incorporate into my commute.

I live in Sacramento, CA and the morning part of my commute is no problem, 3.5 miles at 65F-70F. When I get off work though, its high heat time around 98F or so. The forecast for this week says we'll hit 103F by Wed or Thurs, and i'd like to be prepared. I've started to get mild headaches lately since the heat has been steadily increasing and I don't want them to hinder my riding. Thanks all again for you suggestions, very cool