Egg Cracker
To build it I took a piece of wood, found the middle, and laid a tiny piece of cardboard upright in the center. I attached that to the piece of wood with a whole bunch of duct tape. I put the bottom of the ruler against the side of the piece of cardboard and duct taped them together pretty good. Then I cut a piece of a wrapping paper tube about two inches tall and set it upright on the end of the board, discarding the rest of the tube quickly to get on to the next step.
I duct taped down the small piece on the end of the board with countless pieces of tape but it fell apart later nonetheless. I took a paper clip and bent it into the shape of a hook. I put it right next to the piece of cardboard tubing and used micro-duct tape to fasten it down.
It was the only thing that didn't fall apart later. I did the same thing to another paper clip on the other side of the piece of wood. I tied a rubber band to the top of the ruler and to the paper clip next to the cardboard tube (finally!).