Top Secret Message Holder

I have a hard time getting rid of little things like mechanical pencil refill containers. They're so cute and useful, you know? Like for making a Top Secret Message Holder. What little person wouldn't like to find one of these on his pillow, in his lunchbox, or tucked inside the book he's reading?

Just print out a little label and attach it with clear tape, then cut out pieces of paper that, when folded tightly, will fit perfectly inside the empty container (make sure to make the papers long enough so when they are slipped inside the container there's still something to grab onto to pull it out). I made my papers 1 1/2" x 2 2/3" but the container sizes vary depending on what brand of mechanical pencil refills you use.