Riding a bike and driving a car. While I didn't really chose to do these (my parents chose for me) they both provide immense use from getting to work, fitness and recreation to exploring the country. I'm glad I learned them young.

Also, I think this has been mentioned, but learning to cook. I never really formally made an effort to learn but my mom is a great cook and I seemed to have absorbed the knowledge/natural ability and over a decade of trial and error I seem to have managed to be decent. Useful day to day and for special occasions. Only downside is eating too much.