For us swimming is also non-negotiable.
DS1 has a weekly drumming lesson. It's something he wanted to do so we went with it. He's stuck at it and is bloody good now (he's 8). DS2 wanted guitar lessons. But lasted 3 lessons. See also karate and gymnastics. He's now got a reputation as a starter in our house. He's 6. He is showing an interest in his guitar again through so we might try lessons again. Music lessons require commitment in order to progress so it teaches them that and they then have the reward of constantly improving. Not to mention the skill of playing an instrument and being able to read music.
DS1 tried Beavers, but it wasn't for him. I think it would be right up DS2s street but you can't get into the packs anywhere near me. DS1 only got into that one as it was brand new.
Both boys have recently taken up rugby and are loving that. It suits them. It's physical, it's outdoors. It also teaches them to work as a team, and how to manage frustrations when things don't go the way they want them to (such as a teammate not passing to them).
DS1 also does ad-hoc climbing and bouldering and is working through the Redpoint Climbing Scheme, meaning he builds on his skills every time he goes. He only does ad-hoc as our favourite climbing centre is near my MIL, so he does it when we visit her. If it was closer I think he'd be there much more regularly.
In terms of an unstructured hobby, DS1 is also a keen scooter rider and skateboarder. He will spend hours at local skate parks honing his skills. Often older children at the indoor (paid) one we go to will give him tips and advise him. There's a sense of community there. It's not a club, but regular visits are needed to allow him to work on those skills.
As you can tell, DS1 is my super physical one. DS2 is equally as happy with a colouring book or some action figures.
The best thing is to let your child lead. If it's not something they are interested in, it will become a battle to get them there every week, and you then become resentful because of the money you've spent.