In all the years I ever went to an open mic night. the more 3 chord songs you know the better. It's hard on an open mic night to get 5 guys there that have played say, Welcome to the Jungle. But if you say has anyone played ZZ Top or easy stuff like that where it's just 3 chords and a variation in the chorus your golden and will be able then to solo and shred a bit on the jam parts. Also look around at the crowd. Are they all younger, older. If you walk up and want to play something from say 2005 up and the guys onstage are in their late 30's. You may not be able to find a song you all can play. Hence that's why the more standards you know the better. Also standards are things everyone that is there just to listen will enjoy your efforts more.