I've never been in a place that issues so many receipts. In the smaller stores, you get a receipt from the person behind the counter for your purchases. You then go to a little booth, where you pay. The cashier writes another receipt, keeps a copy, and gives you the first receipt, plus the one just written. Oh, and it also gets stamped, to show you've paid. You take the stamped receipt either back to the person behind the counter, or to an entirely different place in the store to pick up your purchase. Did you get all of that?
My favorite receipts were the ones we got from the national parks (upper right). And be sure to keep the little ticket you get on the micros: I've been on two buses that were stopped by some sort of inspector, who got on and checked each passenger's ticket.