My list - some appear already: duct tape, cable ties, ear-plugs, sun-tan lotion, a hat, sunglasses, plenty of water, tape & poles to rope off pitch, scotch tape for the camping pass, ticket holder, mallet, swiss army knife, parachute cord, little radio for RLM, ear defenders, wet wipes, anti-bacterial hand gel (no water required).
and lastly - plenty of beer, some common sense and a sense of humour!!!