There are reasons to hide various sorts of prep goods. You may be afraid that your house will be burglarized or raided. You might want to have supplies elsewhere in case your home becomes untenable for some reason. You may simply have run out of room and need to stash some stuff elsewhere. In any event, the sorts of things you're seeking to store aren't the same things as the average homeowner will haul do to the local rent-a-garage place and dump in. You may have guns, ammo, food and so on--things that tend to raise eyebrows and attract unwanted attention.
I'm not getting into the business of how you stash goods so that they will be usable in 5 years. We may look at that another time. For now, I want to deal with the topic of how do you find those stashes in 5 years? "25 feet east of the big rock on the east side of the creek" may have sounded like good directions when you buried it, but the creek bed has moved and uncovered 8 more big rocks in the intervening time. Not good.
GPS coordinates can work; geocachers have been using them for years. But you have to store them in some way. Electronics are vulnerable to EMP, water and leaking batteries to name a few things, while a written list is vulnerable to many of the same things plus theft. It could work, but there are a lot of failure points.
The concept I've selected is the map overlay. It has the advantages of being totally manual, and these days, relatively obscure. Back in the day, a map overlay was made from a sheet of translucent material that was drawn on and then laid over a map so that the map could bee seen underneath. However, since we have the advantage of high tech, we can do something that is easier to read an less subject to degradation from the elements such as water.
First, you will need a large scale map of the area where you plan on stashing your goods. It needs to be large scale so that you have the necessary level of detail available to you to locate your stashes. It doesn't have to be a commercial map--you can draw your own if you'd like. Just be sure to make several copies when you finish.
On this map, select 3 locations to act as registration points and mark them with a symbol. These points will allow you to orient the overlay on the area map the same way each time. This means they need to be in some non-regular pattern--an equilateral triangle would be a bad choice.
Next obtain some laser transparency film. This is clear film in sheets that is rated for laser printers and copiers. I prefer this because it will stand up to heat. You will also want some Sharpie permanent markers.
Lay the transparent sheet over the map. Mark the registration points with a unique symbol. Do not use the symbol you used to designate them on the map! Mark each stash with another symbol.
Bear in mind that the safety of this method lies in the disconnect between the map and the overlay. You can have a single map with multiple overlays, but you'll have to carefully manage your symbology, and you'll have to commit it to memory. Write nothing down. Perhaps color coding the overlays might work.
This safety by disconnect also means that you must store the map and overlay(s) separately. How you do this is up to you, but you must avoid anything that would allow someone to make the connection between the two. (This is why you use two different symbols to designate the registration points on the two different layers.) As an example, you might have the map (labeled "General Area Map" or something similarly innocuous) in one of your disaster notebooks and the overlay behind a picture in its frame. More than one person should know where the two parts are, obviously.
More than one set would be a good idea, although that does complicate how to store the maps and overlays. How to manage this is left as an exercise to the reader.