JR celebrated a big birthday a few weeks ago, and he's notoriously hard to buy gifts for. The kids and I thought long and hard about what to get him and decided to give him a collection of different gourmet root beers. JR really likes a good root beer (his favorite right now is Virgil's). Because JR was turning 40, we collected 40 different kinds and added a numbered label to the top of each bottle cap.
We printed the numbers out on label paper (I use the Avery full page sheets that you feed into an inkjet printer) and then punched them out with a 1" circle punch. Luckily all bottle caps seem to be right around 1" wide. While we were getting the bottles ready my five year old Bee remarked, "This is going to be a lot of work when dad turns 100!".
Letters could work too, you could spell out a message or just say "Happy Birthday". If you'd like to make some of your own bottle cap labels, I've made a two page file you can download here. Numbers are on the first page (up to 50) and letters on the second page (which includes two of almost all the letters in the alphabet). Happy Birthday JR! You're going to let me help you drink some of that root beer, right?