People concerned with S&P are often a paranoid lot. I mean, preparing for the apocalypse takes a certain pessimistic outlook on the future. With that quasi tin-foil hat outlook occasionally comes the desire to cache, stash, hide, and conceal items. Food, firearms, ammo, and other tools are amongst the most common items to be hid. Firearms especially, in fear of jack-booted thugs going door-to-door, seizing guns as part of a Hitlery-esque campaign to rob citizens of their 2nd amendment rights.
How to Hide Anything, written in 1984, covers, well, how to hide anything. Many of the hiding places seem to be intended for use in hiding one's "stash" of drugs; if you're worried about someone finding your precious crack stash, you've got more immediate problems than surviving the coming apocalypse. Tiny stashes include the fridge and freezer, under baseboards, drilled out chair legs, behind electrical outlets, and inside piranha tanks.
More useful are the sections on hiding larger items and personnel. Dummy pipework is one of my favorite ideas; unless someone with a good knowledge of plumbing takes a close look at the setup, it can be used to conceal a fairly large amount of preps. Cheap and relatively easy to set up. Creating hidey holes inside sheet rock walls is another interesting idea. Building false walls and ceilings is also discussed. The ideas for hiding personnel include concealed interior rooms and camouflaged bunkers and holes. This size of concealed space may be of most interest to the S&P crowd, in order to pre-cache a stash of supplies on a bug-out land or establish a hideout to use during a bug-out situation.
How to Hide Anything contains illustrations of many of the ideas discussed. They're not detailed diagrams by any means, rather a demonstration of how the idea could be used. It wouldn't surprise me if several of the larger "construction" ideas were structurally unsound. Do your research or check with an expert before making any drastic changes to your home. The book is largely a source of ideas and inspiration for creating your own hiding places, and provides a good starting point for anyone looking to stash a few preps.