1. Collect 20 or so milk bottle caps in the same colour (red for me).
2. Buy two sheets of identical stickers (a gift in our case).
3. Stick pairs of stickers on the caps.
4. Cover stickers with Modge Podge or a homemade facsimile of 2 tsp white glue and 7-10 drops of water.
I stored the whole thing in an empty jam jar.