I always loved fruit machines as a kid and now they are relatively cheap to buy second hand (Shipping cots are a bit wow!) I’ve found them very useful (If not a bit too big) money boxes. It’s amazing how you need to fill it with coins 
The manual that came with it talks about how each unit, coin, reel controller etc. all communicate with the central computer via secure communications and if you tried just putting a new unit in place without configuring the security property the machine tends to yell loudly
Already got £37 worth of £ coins in it.