When I was in highschool, Burger King ran this "checkers" game, where you'd get a card with a little checkerboard on it, then scratch your way across it by picking squares until you either lost or won a prize. The one feature they advertised was that "Every card is a winner", meaning that if you picked the right path you were guaranteed to win something.
A friend had a sister who worked at a Burger King, so he picked up a huge stack of these cards and spent a night scratching off all the spaces from all of them. It turned out they had a control code at the bottom that could be correlated back to the card configuration, so he was able to put together a cheat sheet that had the winning moves for every code.
All that month, meals for every kid in the school would consist of walking into Burger King, asking for a "Complimentary Game Card", which they were legally obligated to provide. Then, after a minute of consultation at a table, returning to the counter: "Looks like I won a small fries. And could I have another game card?"
Fun times. The kid who discovered the pattern claimed to have won a Carribbean Cruise.