The great thing about Arduinos is that they come in all shapes and sizes. You can also make one for yourself. Instructables user MakersBox did just that, with a tiny, modular Arduino-compatible board that can fit inside a Tic Tac container.
The build uses a handful of parts, including an ATtiny capable of running the Arduino IDE. Once you get everything, you can simply snap the pieces together and stuff it inside an old Tic-Tac container.
What you do with it from there is entirely up to you. If you're not a fan of hunting down parts, you can also just order a kit with everything you need from Tindie.