When paying cash, I leave it while I pay. Moving it before paying just gets attendant nervous. Of course, I go in and pay and come right out and leave. No shopping or lottery tickets for me.
Gas pumps around here have signs against leaving the pump unattended while pumping. I don't know if it is illegal, but it sure seems like an unnecessary risk. Same thing with smoking while pumping. If I'm waiting behind you, while I appreciate your courtesy in trying to not waste my time, but I'd prefer your courtesy in not risking my life.