Here's one of my rules for life:
If you're in a line six-people deep, and someone opens up a new register, the polite thing to do is to allow the next person in line to go over to that register. It is NOT polite when the last person drag-races their cart over in front of everyone else. Also, if you're going to be doing these types of things then please, please do not be buying craft supplies for vacation bible school.