If you have a "giant bonfire" then that changes things a bit. I still wouldn't burn plastic. Foil certainly won't burn. But you can throw things like banana peelings, food, and clothing into a very hot fire and it will turn to ash. You can even throw green wood or soaking wet logs into a super hot fire and it'll burn completely. And I can't imagine trying to make a big fire while camping on the trail just to burn all that crap. But if someone is doing that as a tool to clean up and maintain the trail, then I certainly would have no issue with it.