I think the main problem people will face is overflowing septic tanks and then 70k people looking for places to poop that aren't the increasingly threatening portapotties. Like, day one you're not going to be able tell if that's mud or poop on the floor, and there's definitely going to be urine mixed in even if it is mud. If you were storing your food or water on the ground, um... Good luck

Trash works a little differently, I think. Food trash people are comfortable with dealing with, mostly. I think a lot of the kitchy hippy crap that gets waterlogged will get discarded, as well as soiled clothing. People generally don't want to take plastic bags with poop in them in their cars.

But also some people take the trash thing way less seriously than others, and if you do take all your own trash how willing are you to take another camp's worth?

(Our local one has a clean up volunteer group that goes a few weeks after so that the land can be used as a barley field during other parts of the year, the fact that that's necessary says that there's a decent amount of clean up to do)