Conveyor belt sushi: a bunch of different types of dish (strings like 
blue, flowery, etc. or maybe just integer ID) with different prices.
  
You know the initial configuration of the belt and it moves at a certain 
speed (let's say you label the seats around the belt 1..n and there are 
n plates on the belt.  You know how fast they move...).  

Have some kind 
of "time t, customer c pick up dish in front of them) as well as a list 
of the next sushi to replace the taken ones.  How much does each 
customer have to pay.

There are some variations that can make it easier/harder.  

- We can require people to work out using modular arithmetic, or we can 
  make the times small enough to just simulate everything.

- we can make dish type a string or an integer ID

- we can make prices just integer dollars (without the cents), or require 
  them to deal with cents (we shouldn't have to worry about accuracy either
  case, but not having cents will make things super clear.