Cooking. I didn't begin cooking until 20 years ago. Now I'm proficient with French, Creole, Italian, Mexican, Brazilian, Caribbean, Thai, Pit BBQ and my fav, hodge-podge with leftovers.
Now I love cooking the same way people love golf. My least fav is Thai only bc there's so damn many ingredients in a simple dish.
Playing a musical instrument. Wish I'd kept up with piano.
DIY construction. Especially in your 20s-30's. Labor is really high and being able to renovate a bathroom or kitchen yourself will save 70% of the cost of construction. Plumbing is the only thing I'd never do. DIY can add huge value to a house when it's time to sell.
Take a real estate agent's course. Not to sell real estate full time necessarily but for the perks. Courses are short and pretty easy plus they're often given at night. You'll save half on broker fees for life. If a relative/friend wants to sell, you can get a piece of the action by referring them to another agent even if out of state. Referral fees return 10-15% of that side of the transaction whether you bring the buyer or the seller. You'll also learn negotiation tactics. 3 hours, 2 nights a week for 6 weeks and you're in. Everyone should do it but especially if you're < 40 years old.
That's all for now as I've got a client waiting.