you are still thinking in modern currency terms as in "IOU's" which our currency isnt even that anymore, its finite.
In terms of metals and other items, their value won't be thought of in terms of modern currency. Unfortunately, I a barter economy is usually too hard for millions upon millions, and even thousands upon thousands, to work with everyday. After a government backed currency collapses, you will likely see a barter economy spring up, but eventually it will be too hard to continue living. Instead of wallets and coin holders, do we all want to carry around Army backpacks filled with tools, ammo, guns, etc. since we won't know what any particular item owner will take for a needed item?
So what happens are that people start transposing values to physical items which quantity, content, and quality is known. Precious metals have been used as a store of wealth for thousands of years, because it is rare. Folks aren't going to take small 1 oz. vials of sand or dirt in trade for tools, because that stuff will be thought of as valueless because anyone can get that from their yard, desert, or beach.
If such an economy emerges, folks will give more value to the pre-82 pennies knowing they contain more copper than zinc. That's really the only reason to store those vs. current day pennies.