TOD
Oy. Can I choose more than one? I look around me these days and see people -- not just pros, but local friends who dived into multiple instruments back when the diving was good for them -- and I very much wish I'd worked on at least a couple of others.
In high school for some reason I became interested in flute and piccolo, borrowed same from a friend who wasn't using hers at the time, picked up a fingering chart, figured out how to get a sound out of the damned thing, and played around with that for quite a while. Haven't touched one since, and probably couldn't make a sound on it now to save my life, but to this day I can think through the fingering of something I'm hearing.
Prior to that, I became infatuated with drums, bought a cheapo set, and took some lessons. That lasted about as long as the flute, and I didn't go very far with technical proficiency, but I'll bet you if I sat down at a set right now, the basic four-limb coordination for basic rhythms would still be accessible.
I've never had the slightest affinity for strings. I have the ability to pick up an instrument and hand it to its owner without breaking anything, but that's as far as that goes. So, this leaves us with winds and brass, and I would still love to just get familiar with a few such things. Which won't do the world any good at all, so let's not push it...