A builder who used to lose heavily on Fobt's 'injected' a note acceptor with expanding foam in a Corals years ago. Bright orange the stuff was. They tried fixing it but to no avail, and the following day it was wheeled away and replaced with a shiny new one.
Mini cheddars have near perfect dimension and, when coated in BBQ sauce for example, could wreak havoc in any mech.
Excrement is so often overlooked in these scenarios. A stool of appropriate viscosity could be piped into coin and note mechs and is sure to see the machine removed?