Survival skills.

Not necessarily stuff like hunting and dismembering animals... but basic trades skills go a loooong way. Being able to do basic wiring tasks without ending up like the "how did you know my nephew's home burnt down" meme, woodworking, metalworking, painting, plumbing, maybe some basic car maintenance like changing tires, checking important stuff such as tire depth, tire pressure, operating fluids... soooooooooo many young people have zero skills in manual labor and have to call in tradespeople for everything.

That and how to find solutions for problems using Google are the most important skills my father taught me, and that is what I plan on teaching my children one day.