I volunteered at Glastonbury several times in the late 90s. It was big then, the week before the punters came was brilliant. You could still have fires (wood was provided), people would go round selling mushrooms and little cakes, and no one had a phone.
By Sunday the whole place stank, toilets and food waste mostly. Mountains of stuff was left behind. Monday morning a we went round scavenging the good stuff. The travellers took a lot also, the rest went to landfill I guess.
I personally think the organisers of big festifals should make sure there is less waste. Festies like Glasonbury and other big ones are disgraceful when it comes to waste and recycling. The Green Gathering does it very well, but that's very much down to the attitude of the punters as well as the organisers.