When I was in middle school, my parents got introduced to the niche world of background acting. The people you see in the background of your favorite show? Yeah, they all have to sign wavers, take last minute calls to set, and (sometimes) aquire an agent.
Obviously this is only the kind of thing you can do if you live in areas where a lot of film and television is shot, which I did at the time.
Since I was a kid, I mainly did Disney Channel and Nickelodeon shows, most notably Bunk'd.
But I also found myself on the sets of stuff like NCIS:LA, Superwoman, The Middle, as well as various commercials.
According to my aunt I once ate lunch with LL Cool J, though I was completely oblivious at the time.
EDIT; I found an old photo of me using one of the cameras on the set of The Middle. They were shooting an episode at a theater.