The best ones are changes to the environment that push the costs of the other person's actions back on themselves. So have your own toilet paper roll, your own shampoo, etc. If they leave theirs out, move it into some inconvenient cabinet, or put it on their bed. Something that makes it something they have to deal with, and annoying, but out of your way. Same for dishes, if they leave a bunch piled up, move them to their counter (if you divide), into the cabinet dirty (if they have their own section), or into their room.