Three things that should be taught in high school...
Ok, this might be a little optimistic but I think you could get the basics out in a final year class. I know a lot students have a hard time with polynomials but a linear regression should be teachable in context of statistics. Error analysis, confidence intervals, the Gaussian distribution, these are important ideas that would greatly affect society's perception of the world around them, the data they are bombarded with daily and teach some critical thinking. Which leads to...
Sadly, this one is being taught in high schools (at least it was in mine). I recall going over geometric proofs, English comprehension tests, some basics of the scientific method in various science classes, however, I don't think the tools are there for students to pull the gist from these lessons. I think and introduction to logic would be useful. Once they have a grounding in that (I mean a rigourous one) I think you would get a lot more out of all the other classes.
CPR and First Aid
Imagine a population of citizens where everyone has at least had exposure to some first aid and knows the basics of CPR. I've had the class and you're certified only for a couple years because after that you forget exact details. Who wants to get that wrong? That said, is there anything in there that a graduating student can't handle? A whole generation with that knowledge walking around. Surely, it could only be a benefit. It would perhaps be a foundation for future refresher learning as well. Even if they are only good for a few years, there's always another batch coming through the ranks. As the saying goes, "I keep getting older but the eighteen year olds always stay the same age." But, uh, that's in a different context, I guess.