Don't worry, Some1...you'll probbaly have a good time in spite of us.
Remember the following rules of thumb-
Drink twice as much water as you normally do.
Eat light but often.
Booze in 100 degree outdoor heat will get you wasted three times as fast.
Cops lie.
Bands that sound good loud will only sound good outdoors if you're near the stage.
Acoustic bands at large outdoor festivals with a varied lineup sound bad unless the sound guys really know what they're doing. If you like them, catch them when they play near you in a smaller venue.
Don't take anything valuable or irreplacable. Shit gets lost real easy. If you have a nice camera, leave it at home and get a 80 dollar joint. If you can remember, try to pull the card out when you aren't using the camera and keep it in a safe place.
If you can, get a second ID/license now (go to the DMV and say you lost the old one). Carry the old ID and a prepaid credit card with you around your neck. Leave your wallet at home.
Also, prepaid cell phones FTW. There's a lot of advantages to a disposable phone that will become apparent if you think about it for a minute.
Good luck out there.