You already have most things in your camper.
For walking around the festival:
Rug Sack - which should contain:
Ice Packs
Beer
Bog Roll (in case the portaloo has none)
Hand sanitizer (in case it has ran out and you need to visit a portaloo)
Also carry (unless you are really good at standing for three days:
A camping Chair, cheap and light weight.
Never forget:
Wellies
Wet coat
Waterproof boots/shoes
For walking around the festival:
Rug Sack - which should contain:
Ice Packs
Beer
Bog Roll (in case the portaloo has none)
Hand sanitizer (in case it has ran out and you need to visit a portaloo)
Also carry (unless you are really good at standing for three days:
A camping Chair, cheap and light weight.
Never forget:
Wellies
Wet coat
Waterproof boots/shoes