I get the use of currency... but I don't personally understand the gold or silver bar thing in a total breakdown of society situation. It mostly makes sense to me if you are expecting a temporary breakdown of the financial market, but think things will get back to normal afterwards and thus are trying to preserve (or make mobile) your monetary investments.
In the even of a total breakdown, I certainly am not trading my food, tools, animals, etc. for a lump of cosmetic metal.
For most homesteader types, I think labor is the main shortage and something people who are lacking valuable stuff could barter with. But there is a steep learning curve in a society like ours, where most people are so far removed from using their hands effectively. I've met people who I would
feed or pay in exchange for
not trying to help me. (Recalling, with a smile, a certain Thanksgiving where a bunch of the chopped veggies were thrown away because someone thought they were
compost.) Everyone has their gifts, but not all gifts apply in all situations...
Other than that, salt and sugar would be true gold to most folks. I don't eat sugar, but I know from going off sugar years ago that many people would be in a mental/emotional breakdown state if forced to go off it suddenly.
I see examples of this online when you see homesteader types doing these "Eat only what I grew/raised/forage" challenges. The sugar withdrawals people go through - wow! Takes me back... It's a fantastic thing to no longer be addicted to sugar- so freeing - so I guess I'd add that to the "be prepared" list.
All food tastes sweeter, and you are satisfied with a few bites of fruit if you have any at all. My husband has had a blackberry, a raspberry, and a small piece of watermelon this year, and that was a LOT of sugar for him now.