How about the mechanism that opens the swing arm/gate when you leave the camp?
Going back to the Aircrew knife, the curly bladed one was brilliant for opening peach, curry, peas & irish stew tins when the tin opener was missing. Throw it all in the same pot - magic honkers stew at o-my-stupid-o-clock in the morning on a scramble (alerted by hooters not by pager or soft-ring telephone call)!!