Some festivals won’t let you in with a wheelbarrow. Others will, then someone’ll nick it. Best not really. Sledge works, if you must, but if you can’t carry everything on your back you’re taking too much crap.
Camelbak works very well, but don’t plan on filling it up outside the arena, good chance you’ll get searched (Reading and T in the Park won’t even let you take in water)
Don’t take anything you can’t afford to lose or get nicked- petty crime in the campsites is pretty common.
if it rains, something to sit on- even if it’s just a thick carrier bag- will be fantastic. Festival sites turn into immense swamps if it rains.
See if you can get the running times off the net in advance, otherwise it’s usually a tenner for the programme.