Here’s how it works: When you place an order that includes french fries, there is a person behind the counter whose job it is to throw one or two smallish fries into the bottom of the bag, to be found at the end of your meal when maybe, just maybe, you’ll still have a hankering for a fry or two.
The exact procedure varies from chain to chain. At McDonald’s, for example, the fry tosser is generally positioned near the deep fryer, whereas at Burger King, the fry bags are pre-filled so that when you order a meal that includes fries, the server simply uses one of the pre-filled bags. The accidental use of one of these bags explains why you will occasionally find a fry at the bottom of your bag even though you ordered onion rings. Hardee’s restaurants actually have their servers pull double-duty and throw in the extra fries themselves.
The reasons for the existence and persistence of this custom are not entirely clear, but as with most things of this nature, the basic explanation has a lot to do with inertia and tradition – “We do it this way because that’s how we’ve always done it.” Antecedents go back at least as far as colonial times. A young Benjamin Franklin made a diary entry in which he spoke of a trip to the local market, excerpted here:
“I laid in a stock of beans, an order which Mr. Locke expended considerable time in filling … upon examination, I saw that he had placed a few bedraggled beans at the nether end of the bag … he responded to my query with a hearty laugh, saying only, ‘Why my lad, such has been the custom since my father’s father was an unshaven boy…’ ”
So the origins of this custom remain a mystery. If any of you have any additional historical data on the subject, I hope you will share it with us!