I just made 13, I am looking for more film canisters. I used Avery 5162 labels. I copied the one I found, it said:
"Cache In/Trash Out"
Contents: 1 trash bag. Please use the bag to carry out trash from the trash area, the refill this container with a new bag and drop it off in another cache.
Good luck...
You can make your own labels with this free template. http://www.lildevil.org/trashcan