Travel as light as possible: Tent, changes of clothes, bog roll, sleeping bags, torches. Nice and light.... then take as much booze as you can carry.
Decant your spirit of choice in to 2 litre bottles (empty coke ones, etc) and take some mixers. I'd take a few cans of lager, but not many. Chances are they'll be very warm very quickly and be heavy to carry from your car to the camp site.
Don't take anything you can't afford to loose. There's allot of theft at festivals so if you'd be upset at something going missing, then don't take it. I'd especially say this for a festival like Leeds as there is a higher quotent of idiots than at most festivals (16- 18 year olds who think the height of comedy/ being a hardcore rocker is to go get plastered on Stella, vomit everywhere, steal things from other peoples tents and burn other people's tents).
It's an amazing festival and has had some of the best line up's ever, but there's always a high muppet quota that you'll have to deal with that I've not come across as much at other festivals.