With 90 degrees F temperatures coming 'round here in NJ, I thought it'd be helpful to post this. Everyone here knows to drink water while riding, but a recap won't hurt.
Be careful riding in the heat. Drink water often, cool down if you feel you're overheating or having trouble thinking straight. Listen to your body. My rule of thumb is that, if I'm having trouble remembering to watch the road, or keep a good distance from parked cars, I pull over.
This article is a pretty good summary. Links to a lot of tips on how to detect heatstroke, and how to treat it. Also, make sure to ingest something with salt and potassium. Banannas are good. Lightly salted nuts arte good as well, but they tend to get caught in the throat, so you have to , yep, keep drinking water. If your pee is clear you're doing well. And if you don't have to pee, keep drinking until you do. Anyone know if protein intake has any effect on heat tolerance?