Or are the guys at the FBO just f'ing with me?

The thing with the keys, paperwork, hobbs logs, etc. for a rental aircraft.

What's the origin of this term? Google searches lead to nothing but other
senses of the word "can" and online slang / dictionaries have nothing
either.
Is it an acronym? How pervasive is the term? Where does it come from?

Past the can...
T