For one of my classes, I have to conduct a 20 min game/activity with the class that explains how blockchain works in an easy-to-understand way. Would be even better if it has to do with marketing, as that's the class I'm in. It can be as rudimentary or as advanced as we want.
Only idea I have right now is playing a giant game of rock paper scissors where everybody frantically runs around for 10 minutes and plays & wins as many games of rock paper scissors with classmates as they can. When each game is over, both opponents have to go to the notebook in the center of the room and put a tally mark next to who won. This shows that blockchain ensures accountability, everybody documents every "transaction" that is made, and that everybody has access to the public records at all times. (Rather than just everybody keeping track of their own score, which could induce cheating.)
Any ideas? I feel like this is a fun question to answer.
Also Scrabits - which I tried last year with some students. Took a while to get started but also helps with the transaction log, how your whole Bitcoin is returned to you as "change" and, as the author of the article describes easier if you slow it right down and take turns. At the same time explaining that in the real world model everyone is looking for (mining) a valid chain at the same time.