"Though an impoverished person wouldn't be shopping in Waitrose."

More fool them! I've had many a phenomenal bargain in Waitrose on bread, potatoes and superb free-range chickens at the end of the day of the expiry of best-before. I'm talking about twelve-quid chickens, weighing over five pounds, for six quid and two-quid bags of perfectly good spuds at 10p. Packs of "premium" bread for 10p. You never know which day the bargains will appear, but as long as you have some hovering time...