We see this typically more around the Halloween and Christmas when sites are decorated heavily, that being said, it's "technically" (according to the campsite decorating rules) not allowed. That being said, do they enforce that, typically no. They put out signs telling folks it wasn't allowed during this last Halloween due to COVID.
What I've seen other folks do from other groups is they will leave different things like stickers or small trinkets at bus stops and things like that for folks to find.
We've never left anything out but as far as how much, it would depend on when you were going and how much you wanted to spend. If you had any left over, I'm sure you could find enough cast members to spread the love to.