@missy and @rambo, 3 things i think everyone should know how to do.
man, this is a tough one. not coming up with things that everyone should know how to do, but prioritizing them in to a list of the top three. there are so many different factors. for example, everyone who drives should be able to pump their own gas. i'm looking at you, Oregon! so, i will make a list of the most pertinent for my lifestyle.
first off, everyone should know how to share the road! by that i mostly mean passing in the passing lane, and cruising in the travel lane!
secondly, everyone should know the basics on cooking their own food. the difference between using high heat and low heat, how to flip an egg or pancake, what does and doesn't need cooking (bacon prepared properly is safe to eat right out of the package,) and what the temperature danger zone is.
lastly, basic repairs. this is a generally broad statement. i suppose, for my application, this should be listed as a knowledge of simple machines. the basic ones. lever, pulley, wheel, inclined plane, and a few others. anyone should be able to screw in and unscrew anything from light bulbs to shower heads. anyone should be able to screw in a protruding screw in the wall. everyone should be able to sew a hole closed in a shirt or sew a button on their pants. those are basic repairs as well, just done to fabric.
so, there it is. my silly list of knowable stuff. not a good list, but they seemed important while i am typing.