The mischievous course of action if the person's a completely annoying arsewit, of course, is to report their abandoned basket as a bomb threat.

Generally, I agree with the principle that you need a person to hold a place in the supermarket queue, not a basket. People violating that principle annoy me less than (a) those who faff about packing, paying or using a self-service checkout, and (b) those who try taking a trolley through a basket-only queue.

A notable exception is if you notice a damaged item in one's shopping, by the way. The supermarket will try and send someone to get you a replacement, but you can find it much more quickly yourself. Even then, I'd explain to people what I was doing rather than vanishing without warning.