Before starting actual work, I did a couple of summer jobs when I turned 16. I worked as a do-it-all-guy in my city (gardening, cleaning the grounds, etc), and then at a metal factory in Switzerland, again mainly cleaning metal pieces, loading trails of metal pieces, straightening metal pieces… well, you get the idea.
Not very interesting and definitely not related to Computer Science, but you really appreciate to work in an office after you’ve been through working at a factory.