I'm getting ready to graduate high school now, so my working experience is limited.
My dad owned a music shop for several years and I went with him for the day on Saturdays and assisted him with fixing amps, guitars, etc., as well as housekeeping. Highlight of the day was going across the road and getting hot dogs for lunch.
I do odd jobs for my grandparents and for a busy couple. I mowed the lawn at a church for a couple years and do yardwork for a couple neighbors off and on.
Last summer, as my first real job, I worked full-time for several weeks as a carpenter's assistant, where, at a few different locations, we built a porch, redid a floor, installed a few windows, patched a rotted wooden floor, and started demolishing a church's finished basement to prepare for restoration (that was the reason he hired me; he was behind and had to finish that job by a certain date). I enjoyed working for him and learned a lot, and I liked the fact that, as opposed to school, what I did was helping people, and I could sit back and look at my handiwork.
I'm currently doing a Network Plus independent study with my school's IT department. There are three other guys doing the same thing who also go there in their spare time and do odd jobs such as troubleshoot problems, reimage computers, build new computers, etc. (which is the kind of thing I'd like to start a career in), which I also do, but I have less time and am an "extra" person, so they can't pay me, but that's OK... gaining knowledge and experience is what counts at this point. I'm taking PC Repair at the same time, and I love how so much of the information overlaps.