I'd be in the SOS Brigade.

I'm not much of a sports guy, but damn it, archery is bad ass. Heck I'd even take kendo.

Sports, I don't know if many japanese schools have handball clubs like we do though...

If they don't, I would just play football.

Swimming club. Especially since the swim clubs in manga seem much more laid back

I'm in robot club right now, but I'm in college.... Anyway, through my experiences here, I conclude that going to clubs would reduce my free time to non-existence. Thus if I was a high schooler, I'd be in go-home club (If clubs are not mandatory anyway. If it is then maybe kyuudou?).

Well, in reality I was in a Science Club and a robotics club, so that's what I did.

I was also in the "Math Club" but that was just taking a few extra tests each year.