Via Seth Godin's blog, the idea of Ogori or generousity.
A cafe in Japan has some interesting rules:
In a nutshell, you get what the person before you ordered, and the next person gets what you ordered. Thus, if you’re in on the game, you can choose to be either a generous benefactor, and treat those that come after you – or try your luck at being cheap. Either way, it’s an interesting experiment that explores surprise, kindness and encourages interactions.
Read about the experience here. Then ask your students what they would order or to try their hand at writing the story from the perspective of one of the other cafe customers mentioned in the blog post.