Whistling properly and tunefully with trills
Electricianship
Carpentry
Plumbing (these last three, and maybe also the first, should definitely be taught in school, along with cooking and sewing and basic knitting and crochet)
Roller-skating (used to be good at this as a kid, but can't work those new single-line skates, and have never found a hall with a lunge so I could be harnessed in and saved from falling while I learn the trick of balancing again)
Gardening - or rather, controlling the garden, which has bullied me into leaving it almost completely wild
Playing the fiddle, or indeed having enough rhythm to play any instrument
Dancing, ditto; I not only have two left feet but appear to have a third and fourth that tangle them
Navigation - having a proper sense of direction
Recognising faces, and instantly being able to recognise and remember someone I've met years ago (or even days ago)

As for riding a bike, it's easy enough to learn as an adult; it should only take half a day, if that. You get a bicycle that's a little too small for you, and lower the saddle so your feet are touching the ground when you sit on it, then you scoot along. Keep doing that, try raising the saddle a little bit so your toes are touching the ground and keep scooting; when you're confident in this, try using the pedals for a stroke or two, then pedalling steadily. Then move up to a proper-sized bike, and by the end of the day you should be pedalling along properly and enjoying it.