Welding
Rudimentary military tactics such as overlapping fields of fire, how to flank an opponent.
How to grow foodstuffs.
Basic economics (how the world works)
How to start a business.
How to plan a military campaign.
How to steal a kiss.
Even if they never do it.
There are already to many half a$$ welders!
I welded a steering knuckle back on to a JK with two batteries some rod and jumper cables in the outback - that held forty miles back to town on dirt roads. Not some pansy MIG weld in a clean shop!;-)
How to plan a military campaign.
At what level? I deal with high ranking military personnel every week that have no idea how to plan for operations AND support and time phase the required elements.