Vending machine

The things you find out on the internet!

 

YZ stood for 'wise head' - hence the (faded) graphic of the owl at the top.

 

Someone also said if you watched the machine you could tell when the free packet was due to come out. You'd have to be pretty desperate and/or have a lot of time on your hands for the sake of one old penny's worth of "spiggy".

Done