I respect this will be different for each child, but for girls:
Swimming and driving as life skills (was driving around the farm at an early age).
Ballet and/or gymnastics for excellent posture and an awareness that the body is strong, capable and that repetition of exercise can make it achieve remarkable things, usually at age when most girls might get the opposite message around their body. (I accept others might get the complete opposite from these, but that was not my experience).
Piano (or any musical instrument) for the skill of reading music, and the skill of learning something and doing exams independently of school and your peers. Kids do so much in teams (great!) but this often teaches that the time put into piano lessons equals a high distinction vs a pass or fail. And does so in something that ‘doesn’t matter’, ie not school, just an extra curricular activity.
Netball for team work, and a common team sport you can when you move to a new place - often colleges/unis/workplaces might have a netball team and if you are good it’s great way to stay in shape and meet people. Also, if you do the umpiring course kids can gain confidence and make money from it. I’m sure other sports may have similar.
Scouts/Guides etc - great to meet more friends outside school to have strong support networks if the friends in school ever leave/change/gang up on child. Excellent practical life skills they are unlikely to learn elsewhere, and so helpful to suddenly find they know who to pitch a tent, first aid etc. Gives them confidence too, both in having lots of skills they know how to do, and in learning those skills and being aware it is a learning process.
Also a love of reading - best gift you can give a child. Book clubs, reading clubs, library visits every Friday….
Public speaking confidence - Mock trial, public speaking groups etc. So important as a life skill.