Been a few times back in the 90s / early 00s.
Don’t take anything you don’t want nicked.
It’s all a big trade off between how much you want to carry in and how much you really need.
Personally I took a tent, roll mat, travel pillow, torch a wallet full of cash, a slab of Stella, some deodorant wipes (for a squaddie shower) and and an open mind. Take a hat and some warm clothing for the evenings and leave your wellies in the car.
The long drops are far more pleasant for a dump than the portaloos (there used to be a very little used long drop down by the cinema).
Take a bottle of antibacterial handwash. Wash your hands with this before eating.
Go with the flow. Explore off the beaten track and don’t beat yourself up about a timetable to see *ALL* the bands you must see.
Have a great time. I’m almost jealous but will be watching it from the comfort of my living room again.