Maybe some things can be "hidden in plain sight" like "antique collectibles." I've thought of a high shelf in the laundry room with things like a galvanized tub, an old-fashioned wringer, washboards artfully arranged on the walls... In the kitchen, if you have room above the cabinets rather than a soffit, things like a manual grain grinder, small butter churn, vintage crocks (filled, of course) "hurricane" lamps, etc. You're an antique collector, not a prepper. Of course, if the lights go out, your collection is useful...
For your high shelves and the tops of bookcases, attractive decorative baskets (filled with preps) and then topped with silk/artificial greenry or flowers...just look like home decorative items. Ditto for large vases, "vintage" trunks/suitcases/hatboxes...the list goes on. This especially works if you have high ceilings/shelves.
Collect "antique" trunks to use as coffeetables/end tables...fill 'em up.
Make a top shelf of your den built in bookcases look like custom stereo speakers...only it's a false front...preps behind it.
I know ppl have already mentioned filling the box springs of the mattresses, but I'll mention it again...I loved the idea.
Limited uses due to the heat, but what about under the rolls of insulation in your attic?? It isn't optimal, but it's a possibility if you're desparate for ideas...
For the bulk foodstuffs that are undeniably preps, maybe a false wall in a deep closet?? This would have to be for very long term things like grain, as it won't be easily accessible.
Last but not least, an inventory of where you put all this stuff!!!
