You want to save like they do? I bet you're capable: Save all your best coupons for months. Steal newspapers so you can get more coupons. Save up store credit vouchers, whatever you can get. Once you have all that, work all week to engineer one "perfect storm" of a shopping trip. Choose a store that price matches. Spend six hours in the store. Come home with a basketful of processed food items that won't make any real meals.
Oh, and when you come home, announce that you have "saved" $500 or so. Of course, the reality is that you'll have $20-50 less in your checking account, so the "saved" money is rather hypothetical. To buy into those "savings" you must figure up the retail cost of the items you hoarded, I mean purchased. Since most of us don't need 99 bottles of mustard, the actual useful value of those "savings" is questionable.
Of course, you know the truth: In the real world, you cannot do this over and over every week. It's not possible. But, for one shining shopping trip, you can LOOK LIKE you're saving 90+% off your bill.