One remarkably simple thing we do is bring a thermos with coffee, as opposed to the fast food variety. I'm disgusted every year seeing styrofoam cups all over our lake, surely from people who forget that in a good breeze, styrofoam blows out of the boat. I also have many golf towels from outings, and the hooks are perfect for most rails, so I use one to hang a drawstring canvas bag from a side rail for garbage.
Well, as much as I shouldn't have to, I often come back with a pocketfuls of abandoned line and empty beer cans in my creel. People should be responsible for their own crap.