On a side note - I also keep a Nerf ball in my desk drawer for Silent Ball. If you haven't heard of this game, and you teach middle schoolers, take note! All students sit on top of their desks. One student is handed the Nerf ball and they toss it (underhand) to any other student in the room. If the student catches it, play continues. If the player does not catch the ball because the toss is bad, the thrower must sit down in his/her chair and is "out." If the player misses a ball that is thrown well, he must sit down in his chair. Play continues until only one champion remains. A couple of notes: If you fall off your desk (thrower or catcher) you are out (you may get off your desk to retrieve a ball on the floor). Balls must be thrown underhand and anyone who talks (other than to QUIETLY discuss which player should be out) is also out of the game. I always encouraged the kids to police themselves and they often would just sit down when they knew they'd thrown poorly or missed the catch!
Good luck gathering activities for these type of extended periods!