Bring (in no particular order):
Something to sit on
Flashlight and BATTERIES (won't need it for getting around, just finding stuff in your tent or car)
Bug stuff
Sunscreen
A hat would be good
Rain gear. Lots and lots of it.
Towel, washcloth, soap, shampoo, and all that sort of stuff
Enough sweaters or jackets.
Snacks for when you're hungry at 4AM, the food places are closed and you're not quite crazy enough to cook something.
Towlettes or baby wipes (those moistened thingies) can come in handy
Headache stuff/stomach stuff/prescription meds
A water bottle, or you can buy one and keep refilling
The thing I most consistently forget: hammer for tent spikes

I hope to get there early Fri afternoon. I'll probably forget to pack my clothes. ;-)