1. Hydrate
2. Hydrate
3. See #1 and #2

If you're thirsty, you're already behind.

Also, don't go out too fast.

Train like you will ride in the event. By this I mean, wear what you will wear, drink what you will drink, don't put any new parts on your bike at the last minute. The last place you want to find out that the cool new shorts you bought are rubbing your "parts" wrong is at mile 40.

SUNSCREEN!!! Even in partly cloudy conditions. Be sure to cover the places you might forget, like the back of your legs.

Food that I find works well...

Fig Newtons
Raisins
bananas
clif bar/powerbar
Gu shots/Cliff Shots
bagel (can be hard to chew if your mouth is dry)
trail mix

eat small amounts at a time. Also, try eating on a shorter training ride, so your stomach gets used to having food in it while you're exercising.