Jokes aside, carpentry is an amazing complementary hobby for software related work. There's something about drawing on a piece of paper and using your hands to make it a reality that scratches a lot of itches.
Sadly, entrepreneurship doesn't leave much free time for carpentry.
Getting into manual machining is another good one. If you go into it with even a hint of a "move fast and break stuff" mentality you'll find yourself mostly just breaking a lot of stuff. It's good practice for being deliberate in your actions.
