When having unproductive moments, I look for quick wins!
Quick wins are small things I can do, and finish (very important!), in a very short period of time, like 2 or 5 minutes or so.
Doing those quick wins, will get your mind switch to a positive mindset of accomplishment, and the pleasure that comes with that. And it will make you want to accomplish more.
Et voila, before you know it, your unproductive moment has turned into a productive one ;-)