Sometimes at open mic's, you get help from other musicians. At Patti's 410, which has their open mic on Thursdays, we often have bass guitarist, Al, back us up...
...and, if there's a drummer handy, we get that kind of help, too.
Many times, though, if Bill's not available and I feel the courage to go solo, I will get up and do some original material. I heard, once, that your songs aren't good until you hit your 1000th. I'm so far from that many that I will likely be churning out crappy songs for some time. I do think, though, that they keep getting better, so I'm encouraged.
So, even though my ears still feel some discomfort when the music gets loud, I can tolerate the quieter acoustic sounds.
What's really been nice for me in the last year is that I've met some really nice folks in the open mic scene. We all keep showing up, encouraging one another, and listening and learning.