You should try a cup of tea or hot chocolate before the show. Hold it with both of your hands and drink it slowly. That helps you to calm down and concentrate on the set and gives warmth to your fingers as well.
Do you smoke? - this will cut down the circulation and could contribute to your hand problem.
Puppyonacid has got it right - during the time (8 years) I studied Karate I trained 4 times a week min - gave up smoking and felt great. - but my guitar playing suffered 'cos I just gave up playing!!
It's true that exercise and good health help a ton. I've always been active, but I took up boxing a few years ago and it really helped with the circulation. (Plus it's nice to kick ass from time to time when you're sparring ... well nicer than getting your ass kicked ...)