I'll echo the drink water sentiment. Take your water bottles (note the plural), fill them partly with water and stick them in the freezer. When you ride, Fill them the rest of the way with water so you can keep cool.

Also, drink a full bottle or a few glasses of water about 30 minutes to an hour before you ride. You want the water out of your stomach and into your cells and blood, where it will do some good.

I second the shirtless idea too. If you're as pale as me, you get the bonus of being really easy to spot.