While a few touring bands have their own roadies, most simply hire locals to handle things like setting up sound systems and lugging equipment. Doing so keeps their costs lower (they don't have to pay for travel and accommodation), and you can take advantage of that. If you've got a little muscle and don't mind getting paid $100 or so for a few hours of work, then make yourself available as a local band roadie. The best way to find these jobs is to hook up with PA and musical equipment rental agents in your town, or with concert promoters.
Promoters can be a great resource for this type of work. If they're good at what they do, they're always busy, and you'd be surprised how easy it is to get hired if you simply show up at the right time. It's a matter of putting yourself out there, being willing to work, and showing up when you're supposed to. If you do that, you'll be far ahead of most of the people looking for roadie work, and eventually the jobs will come looking for you!