Cache sounds like what it is, a stash, and sometimes people — usually the criminal type — have a cache of stolen cash.
Often the phrase "weapons cache" is used of a bunch of hidden guns or weapons that have been hidden or stored away, which is logical, given that the French verb cacher means "to hide." Sometimes things aren’t really hidden but are stored away out of sight for use later. Computers even cache data and directories to retrieve when needed. So a cache is anything from a stash of cash to a store of information on reserve.