I included the jobs I had in high school (they specifically asked what jobs I had, and I figured starting work at 16 might make me look special), but beyond that, nothing.
Once you get here, undergrad is kind of a joke (not to belittle your experience at all, I simply mean that it's a running joke that if people here put in the effort they do now when they were in undergrad, we all would have had an easy 4.0), in much the same way that high school doesn't matter when you're in undergrad.
If you did something substantial (like cultivate a bacteria that would degrade styrofoam exponentially faster...crazy kid) then put it in there, but if it's not Nobel prize worthy, best bet is to leave it out. Like doob said, though, including most anything medical can't hurt.
Good luck in your endeavors!