The Ultimate Camping Survival Guide for Festival Season

Clothing:
You probably won't need much. Store one outfit in a plastic bag to keep dry in case it rains. Don't bring anything worth more than a few bucks, as festival clothing gets ruined easily.

A few T-shirts, and sweatshirts.
Two pairs of shorts, one pair of jeans, one pair of sweat pants.
A bathing suit.
Five pairs of socks.
Two pairs of comfortable sneakers, one pair of sandals.
At least one set of underwear per day.
Sunglasses and a hat.
A headband or bandana.
Rain ponchos.
You will smell. Bring deodorant.

Campsite Etiquette:
Be a good neighbor. And keep yourself alive.

Give yourself enough room to hang out comfortably, but don't encroach on your neighbors.
Your shade tent should act as your living room. Set up the chairs and tables under the canopy.
Invite your neighbors to hang out. Offer to keep an eye on their gear and they'll do the same.
To avoid spiders and other bugs, don't eat inside your tent and keep it zipped shut.
Be pleasant to security and festival personnel. They'll return the favor.
Share with your neighbors!
Have fun and keep an eye on one another.

The Car:
You want to prepare yourself from the very beginning, which means making sure your ride is in tiptop shape.

Change the oil and radiator fluid, check all other fluids.
Check tire pressure and make sure your spare is in good shape.
Bring a map, know your route.
Clean the entire car and keep garbage bags inside.
Know the laws in each state you'll be traveling through. (Example: As long as you are at least 21 and not driving, you can drink in a moving car in Tennessee.)
Try not to tie anything to the roof. The police can pull you over to "make sure everything is secure."
Don't speed! Cops will be out in full force looking for out-of-state drivers.
Security and police will search your car at the festival gate. Just keep it in mind.