It's not exactly letting someone else go first in line, but rather helping the person in front of me. In grocery lines where you have to bag your own groceries, which I think is almost everywhere now, it's often difficult to keep feeding the check-out conveyor and also bag at then other end. So I've been helping the person in front of me by putting the groceries from their cart onto the conveyor belt. At first, there is a little shock that someone is handling the stuff from their grocery cart, but after the initial reaction, people seem genuinely pleased and grateful. I haven't seen this catch on with others yet, but I'm waiting for it.