The best use of the last 5 minutes of my work day, without question, is making a few comments on about half a sheet of paper of what open questions I have for tomorrow and a couple of directions I might head to solve them, along with caveats/gotchas I thought of while working.
This way when I let go of work for the day, I don't think about it anymore unless I really want to and I'm confident that I have enough written down to hit the ground running the next time I want to work.
This frees me up completely to do something _besides_ work.