Bars and promoters like to get as many bands as they can to play in a day. The reason is that each band will bring its own fans, some may come just to see their band's show, some will come a little early, and you better believe they want people to stay late.
It's great for the bars, but what about the 2nd, 3rd, or 4th band in the evening. What if you get there, and here the band play much of your set? How are you going to kick their ass? Will the crowd want to hear "Heart-Shaped Box" or "She Will Be Loved" or "Layla" or "Walkin' the Dog" again?
One surefire way to kickass at a bar is audience involvement. Not kareoke, but something as simple as hand-claps, or repetition, or songs everyone knows but maybe hasn't thought of in a long time, or one-hit wonders. I asked Rockers of rockandrolltribe.com for tunes they'd like bands to cover--but never, ever do.
HANDCLAPS
Not handclapping, but it's got repetition (and hey, is that a handclap I hear in the background?)
DRINKING SONGS are always great. People are there to drink and have a good time. They will definitely be howlin' if you play...
If you have a few RARE OR B-SIDES songs in your pocket, some of the audience might even think they are your originals...
This was originally by The Crazy Teens in the 50s:
http://youtu.be/8Cp8H8PUI08
(embedding disabled)
AND FINALLY...it takes more time and effort, but stealing from a genre you consider opposite your own and making them your own can make some memorable results:
Better as disco or metal?
Better as Old School Punk or Country?
