I've just looked at the empty packet of Salt and Vinegar (Golden Wonder, of course) sitting in my bin, and guess what? It's a refugee from a bleedin' multipack! It was bought from a vending machine this very day, and has a miserly 25g as opposed to the standard 30g pack. What should I do? I ain't no grass, but a crime's a crime.
Chillum - I suggest you lay in wait near the vending machine - possibly disguised as a ninja or similar. When the person who fills the machine arrives you can jump out and confront them with the crisp packet.