I have a teenager and a nearly teenager. I'm sure I've forgotten some things I need to teach them before they fly the nest.
For starters:
How to change a fuse and a lightbulb.
Basic cooking skills. Lots of subcategories here - how to make a decent roast, bechamel sauce, whip up a few easy meals, chop an onion properly.
Basic Sewing I'm sadly lacking in this area. Despite my mother's efforts, I can barely sew on a button. Will delegate to granny.
How to tip
How to shuffle and deal cards Admittedly not a biggie.
Most importantly - how not to be an arse
There's lots more, I know.