There are numerous things you can do:
The rubber band trick sounds like it could work. Another solution is superglue/zapagap/whatever'ing the screwdriver into the head, and then unscrewing that way. If your screw is backed out a bit, take a dremel and cut a slit in the head so you can use a small flathead to unscrew it. If all else fails, I've had luck with drilling the head off (using a larger bit than the shaft) and then removing the shaft with needlenose pliers. I'd try that only as a last ditch effort, though, and even then with these tiny screws I'm not sure if that's a viable option.