Receipts are fixed and appended ceipts, which are sometimes included in various bits of clothing, pastry, and insects. If you're lucky enought to find or steal a receipt, you may want to hold onto it, because without the receipt, your toaster or hyena or whatever else you bought will be worthless and you'll have to hang onto it forever, like an albatross around your neck, which you can bet your boots, didn't have a proper receipt.
Ceipts are good for something, of course. Mementos of cherished moments gone by. That first kiss you two had on the Ferris wheel, for instance. But just try getting your money back from the carny that lofted you into the stratosphere without a good, honest to God receipt. No way in hell.
Probably one of the most useful things about receipts is that you can use them to create alibis. Remember that last drifter you killed? Sure you do. If you have a receipt that says you were eating a hotdog in another state at the time poor ol' Wandering Willie got a corn knife in his gizzard, you're off scot free! No jury in the world would convict you.