When I'm the only guitar player/singer around I usually just play stuff as the background music unless someone requests me to play something... Normally it's stuff like Good Riddence by Green Day or something stupid like that... even though it's a good sing a long song because everyone knows the words to it... If it's me and a few friends I get caught playing and singing a lot of Jack Johnson, Dave Matthews, and Ben Harper.... All are a lot of fun to sing with a group of people... and especially effective at courting the ladies... But my personal faaaavorite thing to play while drinking with friends is probably anything by Stevie Ray Vaughan... Texas Flood, Pride and Joy, Scuttle Buttin, Tin Pan Alley, Cold Shot, Superstitious... on and on... After all, it's good drinking music.