Garage Door White Board
I did this mod to my garage door years ago. It's an awesome place to put lists and notes. I highly suggest that you buy the squirt bottle of cleaner if you do this. You'll find that you leave stuff on it long enough that it gets pretty hard to erase. The cleaner really helps. If you don't have the cleaner, you can "write over" the previous writing...basically trace the lines of the letter/drawings and it will "wet" the old lines so you can erase them. The spray is much easier and faster.