When our kids were little (too young to be much help setting up camp or packing up to leave), we issued each kid a garbage back and told them they weren't allowed in the truck to come home until they each filled their bags. They got pretty good at it after a few trips.
After a year or two, they had completely cleaned up all of our favorite camps, including all the bulky stuff like tires and bumpers.
When they were finally old enough to help us back up, they still instinctively made the rounds around camp to pick up any of the clutter. There are always a few grocery bags and old mylar balloons in the bushes around camp. I'm glad to see that the routine was kept alive with them. They're adults now and they still do it.
