TriggerDog has been doing the projects in Making Things Talk, and came up with a great way to take the Arduino on the go:
Small easy, and awfully unorigional. But, useful and free. Now I can bring my arduino with me in my laptop bag and goof around with it at lunch time at work or wherever. I am thinking I would put a breadboard in another tin of some sort and put a battery pack inside to run any projects I might feel inclined to proto.