Arduinos are already pretty small, but they're still not conducive to travelling. Instructables user sath02 wanted to take his electronics tinkering on the road with him, so he built a pocket-sized Arduino kit.
The kit uses a palm-size Arduino board made with an ATMega and a boot loader. From there, it also includes a tiny breadboard, a homemade 5V voltage regulator, and a USB. It's all packed into a tiny antistatic container. The end result is a completly portable, self-contained Arduino kit that can go with you just about everywhere. Head over to Instructables for a full breakdown of all the parts, schematics and directions.
Palm Arduino Kit [Instructables]