I'm a 50+ intermediate beginner and have just started playing a small open mike in my little town. I'm strictly an open chord strummer, while some of the other folks are very, very good. I play what I know and like, it's a lot different sitting in front of people than doing it at home by yourself!
I made a comment one night that I'm not as good as the others, and one gal said, "yeah, but you play fun songs". I almost always do a Buffett song, Johnny Cash and of course some Beatles. People like that stuff and can sing along with it. "Brown Eyed Girl" is another good one.
You'd be surprised at the reaction to fun, simple songs. To quote Forrest Gump, open mikes are like a box of chocolates, you never know what you're gonna get.