Assuredly Stoned Guy Checking Out the Chips
He was there when you got to the supermarket, and he'll be there when you leave.
Small Family with Three Full Shopping Carts
Wait, was there an emergency alert we're unaware of? If so, this family's bunker's gonna be incredibly well-stocked. Become good friends with them.
Depressing Haul Guy
A cursory glance into his basket reveals: a six-pack of cheap beer, a box of mini powdered donuts, some Stouffer's Meals for One, an extension cord, and a pulp romance novel.
Expired Coupon Fanatic
Despite the fact that her coupon is from 2007, she's insistent that it still be honored, and is thus holding up the entire line by berating the cashier.
Parents Using Kids to Get Extra Items While They're in Line
Oh, would you look at that! They "realized" that they "forgot" certain items on their list right when they were about to check out, so they've sent their kids around the supermarket to collect the missing items. The kids will return with the wrong ones and be sent out again, while everyone behind them invariably gets turned into Extremely Loud Sighers.