Coins that are pure silver or pure gold are called "rounds" and you get them from precious metals traders. They are normally encased in plastic so that they do not tarnish.
Currency coins of any other kind have long been debased by other lesser semiprecious metal additives like nickel or copper, so their value is less, and it is a theoretical value, since it takes time and effort and gear to melt them and get the pure metal elements separated.
Coins with numismic value are part of a market that varies due to demand. And demand varies. Anyone who bought and sold derivatives through 2008 has learned all about demand varying.
A nice beautiful collection that is complete has value in and of itself, the whole being greater than the parts. In order to complete their collections, various people will treat certain rare individual coins as valuable.
I have coins from all around the world, in complete sets, from their least penny to their highest 100 currency unit coin. They are only worth whatever someone else who also loves coins will pay for them.
Someday I will give them to a grand niece or nephew. Children are delighted with collections. Children are collectors.
Adults collect ideas and knowledge, and they write books. And books are precious to adults. Even books about coins.
But all these things simply have intangible emotional value.
On the other hand, a cartridge has tangible real value. Because with a bullet you can kill an animal and provide a meal.
A cartridge also allows you to defend yourself.
So make sure you are saving bullets and ammo too.