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.
I wonder how many altoids have sold just for the tin.
Your basic Altoids tin.
Crudely drill holes to accept 4-40 screws. Line with electrical tape, I liked blue.
Drill holes to allow the use of a sheetmetal nibbler (I got mine at radio shack) The cover interferes a little with the connections but they still connect, and I think I will usually use the arduino with the cover open.
Arduino screwed in with 2 4-40 screws and hex nuts.