A cute way to annoy the chair savers. move the "stuff "on one of their chairs a few seats over. When they finally come up on deck they will have their two chairs, they just won't be together. Who are they going to complain to? They will look back and forth at the folks on the 5 or six chairs in between, try and figure out what happened, then they eventually take all their stuff and move off.
Just be careful you don't do this to Rick, when I posted this suggestion one other time he said if I touched his stuff he'd toss me overboard.