The old woman, rummaging through her purse, asks, "What was that again?" and the cashier - a frog-eyed gum chewer with dreads, a Live Strong bracelet, and a nametag-less green apron - says, "Eighty-eight, sixty-six."[...] In line behind her, another customer - an unshaven guy with bloodshot eyes and a ratty tee shirt spelling out the words "Guided by Voices" and a chin that looks as though he's dipped it in beard, a guy who's holding a six-pack of Coors and a shopping basket stacked with three packages of pre-formed hamburger patties - shuts his eyes and lets his head fall backward, as if to say, "Please God, no." The old woman, who looks approximately the same age as the price of her groceries, begins writing - with gnarled, age-spotted, thick-knuckled hands - the name of the grocery store on the "to" line, which means that she, unlike those super-prepared shoppers who've filled in everything but the total before they've set foot in the store, has failed to think ahead.
Literary Review - Checkout by Vollmer Matthew
Could someone explain to me what does the bolded part of the last sentence exactly mean here?
Does this part relates to the shoppers who've ever set foot in the store before, or to the ones who are now in the store?
I can't discern the right meaning!