I'm partial to TDD because it's great for that "simple task"/error-fixing mentality. About 30 minutes before leaving, I make sure I have a couple failing tests and leave them that way when I leave.
Whenever I get back to work, I can just jump in... any kind of work interruption benefits the same way.
This reminds me of a practice Ernest Hemingway supposedly used to maintain his productivity. He would purposely stop writing for the day when he was in a state of flow and knew what he would write next, so that it'd be easy to resume his progress when he came back to his desk the next day:
Whenever I get back to work, I can just jump in... any kind of work interruption benefits the same way.