From the page here:
Will be interesting to see what the take up of these are given that the preference now seems to be for coins & path tags.Ever wish your travel bug had a nice protective backpack to carry that special item from cache to cache. Well now it does. The new Travel Bug Backpacker is a special Geocoin designed to fit onto a traditional 35mm film canister (not included). This is the perfect solution for sending items or log sheets that you aren’t able to attach to a Travel Bug chain. This coin features the Travel Bug logo and comes with a copy tag to keep as a permanent record of your unique tracking number. You should be able to find free film canisters at any local store that processes film.
Each Travel Bug gets its own page on geocaching.com where you can track its progress as it passes on from person to person or cache to cache.