Very Big Gulp
Several years ago, 7-11 ran a promotion where all of the Big Gulp cups had a sticker on them that had some kind of prize on them.
The sticker had those little, wavy blue and red lines that you had to look at through 3D glasses to read, so, in theory, you had no idea what you had won until the clerk looked at it at checkout. Most of the prizes were crap – stuff like 25 cents off of a sketchy hot dog.
But, one of the prizes was a free Big Gulp, so if you got that one, your Big Gulp was free. I memorized the pattern of blue and red lines, fished through the cups until I got the right one and got free soda pop for about two months until the promotion ended. Excuse me while I go check my insulin…
Story credit: Reddit / Troutmandoo