You can legally bartend when you're 18. My youngest son went through bartending school when he was 18, he was still in highschool at the time. He got his certificate and went on several job interviews but nobody would hire him. I think the reason pretty much was because he was only 18 although they don't actually come out and say that as that would be discriminatory.
As for the craigslist idea, I had a friend once who had lost his job but he was able to make ends meet (at least temporarily) by buying electronics on sale and reselling them on e-bay for a profit.