100% Agreed with all said so far, plus...
1. Expect mistakes to happen -- just let them go, recover as best you can, and move on.
2. Your heroes no doubt screwed up on stage countless times (check You Tube, you might find actual video clips).
3. Concentrate on other people in your group who might not be as solid/rehearsed, as you might see your potential mistakes lessen, or not happen at all. As long as you practiced, etc you did your part.
4. Don't drink or take anything to ovecome the fear of mistakes -- your playing will only suck more (record the performance and play it back later if you don't believe me).
5. Chances are, you'll be playing so loud/the audience will be so drunk that no one will notice the difference.
6. "F" the critics in the audience -- you already practiced your butt off (the fact that you have anxiety proves you care about your performance) and let them do better, if they can.
7. Tomorrow is another day to improve your playing that much more -- learn from your mistakes.