I've seen parents and kids playing "I spy" in line. I thought that was a good idea. No equipment required and you don't have to move around with that game.
One of my comoderators, cleo, always carries little bottles of bubbles (like those given out at weddings) and when there is a fussy child in line she will blow some bubbles and it sidetracks the fussiness. I've been with her when she does this and I must admit it really changes the child's attitude. She then gives the little bottle of bubbles to the child, if the parent agrees.
Our cleo is very creative.