The ultimate in minimalist personal railroad sets, this creation can be made in seconds using a coil of copper, set of magnets and single battery. The animated image above pretty much says it all, but you can also see a more detailed video below.
Add a few magnets on either side of the battery then set your creation loose inside the coil and watch it shoot from one end to the other. Coiling the copper (if starting with wire) is probably the most time-consuming part of the equation, but easy to do with idle hands while, say, watching the video showing how to do the other parts.
The result is quite bare in terms of initial aesthetics, but of course you can always start covering things up in creative ways, too, or elaborating on the basic design to make more complex ‘tracks’ for your creation.