I don't need a receipt for a doughnut. I'll just give you...

I don't need a receipt for a doughnut. I'll just give you the money, and you give me the doughnut. End of transaction! We don't need to bring ink and paper into this! I can't imagine a scenario where I'd have to prove that I bought a doughnut. Some skeptical friend...'Don't even act like I didn't buy that doughnut! I've got the documentation right here! Oh, wait, it's back home, in the file. Under d...for doughnut.'