[Osmose]

My personal habit is to play with a small deck of business cards, or sometimes a koosh ball with thin filaments. Both provide a pleasing tactile sensation and are easy enough to mess around with while thinking.

I also find it helpful to use this downtime to review how I've been working. The best thing I learned from the Pragmatic Programmer was to review my coding techniques and patterns, and see where there could be an improvement. Perhaps I spent the last 20 minutes fixing the wrong problem, or perhaps I didn't use a design pattern that would've made my code cleaner and easier to understand. Micro-breaks are a great time for these reviews because the code is fresh in your mind, whereas a retrospective when a release is done requires a lot more looking back.