Pass the cup.
Tomorrow I'm going out for coffee and a bagel with a friend. We're going to a place where you have to go up to the counter to order, pay, and collect your food. I'm going to give the person at the counter an extra 2 dollars and ask them to apply it to whoever comes up to the counter after me.

I'll see how it goes. I hope it's a great, happy surprise to whoever gets it.