By this point of preparation, you can do little to fundamentally change your outlook on the nature of a performance. So your best bet is to set up conditions so that you are in peak shape to perform even if you still have lingering worries.

Get enough sleep the night before. Pavarotti said in Great Singers on Great Singing that on a typical performance day he would sleep in until noon. Rest!
Eat enough….but not too much. It’s scary being so stuffed that you cannot breathe, but it’s equally frightening to be so famished that you have no strength. This will probably deserve its own post in the future, but you must learn what is best for your body and your voice when you eat. Before a performance, try eating a light meal a few hours in advance. Then bring fruit to the performance to refuel while you are taking breaks.
Beware of Caffeine. In my most recent Weekly Gathering, I posted Coffee Breakdowns: Is There a Link Between Caffeine and Hallucinations? This quote is particularly ominous for the potentially worried performer:

Caffeine heightens the physiological effects of stress, lead author Simon Jones says. When someone feels anxiety, the body releases the

…[Continue reading Perform Fearlessly Part IV: The Day of the Performance]