Ds does activities and classes because he wants to.
When he was younger I did have him in acting classes as his major outside activity. He didn't necessarily ask to do these classes, it was mostly just a way to meet other kids and have fun (really play oriented classes) where he could be appreciated for being who he is, rather than punished, like when he was in ps, for being excitable, imaginative and noisy.
As he reached his teens, he's a lot more interested in doing outside activities and will ask for and arrange for stuff himself. This summer he's doing football, and is looking forward to (hopefully) playing rugby, lacrosse and wrestling on a high school team (if the high school will allow an hs student to play.)
He got bored with the acting classes for a while, but now he's old enough to do the teen division courses and has been looking forward for a long time to doing an improv class and, maybe, auditioning for the improv troupe.
He wants to do sea cadets because they will teach him marksmanship (with bb guns, thankfully, this kid hurts himself walking!), they have cool summer camp opportunities, and he's very interested in military history/weapons/tactics.
At his age now, the outside activities are not so much about exposing him to new things, or keeping him busy, as about him pursuing his own interests and likes more deeply. There are a few things I would like him to study (a musical instrument, French) but he's not terribly interested, so there's no point in me spending the money on it at the moment.
One activity I always insisted on was swimming, since we live a block from a major river and several local kids have drowned in the past decade only a few blocks from here. Once ds got to the point where he felt competent and safe in the water, and had reached a fairly proficient swimming level, I let him drop the classes. He never really enjoyed them, but that was a safety thing.
He's done other activities throught the Y over the years, and has been able to discover what kinds of things he loves (really aggresive sports, stand up comedy) and what kinds of things that all his friends love but that he hates (soccer, scouting) and he's fine with that.
As other posters have touched on, when ds was in school, we didn't do any outside activities, because we didn't have time and he was too tired, so all the classes and stuff we've done since hsing have been because we finally have a chance to!
Follow Mothering