Years ago I had something similar that I and my cohorts (ab)used the heck out of.
Near our work was a Pizza Hut. Which was staffed entirely by uncaring incompetent stoners. Who could never hustle; even at the height of the lunch rush they’d be moseying serenely along. Whenever somebody suggested that place for lunch we all groaned about the long wait but went anyhow because … PIZZA!!! And we were all 20-something and stupid.
So World HQ comes up with this great promo to increase sales at lunch: Your meal is ready in 5 minutes or you get a coupon for a free meal next time. Cue lightbulb moment for us.
So we go. They give us a little timer when we order and pay. Sure enough it takes 10 minutes for our 'za to be ready, so we each get a coupon.
And tomorrow we all come back and exchange our coupons for a timer, a 10 minute wait, a free 'za, and a fresh shiny new coupon!
We ate free 'za every day for about two months!
Eventually we got tired of all the crappy 'za and only went every week or so. About six months later World HQ came to its senses and terminated the promo. But not before we’d beaten them like a red-headed stepchild.
Soda was IIRC 75 cents for a 12 oz. plastic cup and infinite refills. Some of us even skipped that and had free water instead. So it’s not like they were getting rich off that either.