Cooking.

Learning how to prepare foods. Nothing fancy, but I find it a stress relieving activity. Then I get to eat at the end. I learned from watching Good Eats, where the host broke down the science behind how the food is cooking and why you do certain things. Like cutting a steak with the grain vs against the grain.

I think J. Kenji Lopez-Alt with Food Labs is a more modern version of Alton Brown. And a little less pretentious, but I'm sure there are others. Cooking is an art. Learn the basics and you can throw together all sorts of food and make it taste good.