Proving you're not getting duped with plated lead is actually pretty hard to do without high technology, hence the reason gold coinage came into existence and then gold depositories and banking and all the rest.

Gold is transitorily convenient provided you exercise military force over a domain - that is you can force gold to be accepted for debts within your dominion. Nothing about it makes it intrinsically valuable otherwise - and more importantly you having gold doesn't grant you wealth because you didn't economically contribute to the system to start with.

Turning up with all the gold you want would get it rejected or siezed because it wasn't an approved coinage.

As an intermediary, currency requires a minimum amount of social relations. Its value, if it can be said to have one, lies in its use as an indirect measure of the degree of faith in a particular set of social constructs.

The reason I use the post-apocalyptic scenario is exactly because of this rupture of social relations. It is not the ghost of the previous civilization trying to reconstitute itself. It is a place in a wilderness onto which people might stumble. (Admittedly, this might not be communicated well and too informed by my early secondary consumption of old western movies.)

Without this broader social context, the concept of trade becomes purely localized. My needs are not serviced by an explicit diffuse network which is conceptualized as an aspect not just of society but constitutive of reality. Operating on a faith, we take the conceptualization as reality and can accept, in our lives now, intermediary exchange: I firmly believe that by accepting an electronic transfer to my bank, I will be able to buy sweet and salty food that is engineered to appeal to my dietary obsessions as bequeathed by a combination of evolution and social conditioning.

In the midst of such a thought experiment, however, I am not guaranteed to encounter another haggard individual in this hypothesized godforsaken world for a very long time. Neither am I guaranteed that any individual I meet will have such social relations as to value such an intermediary, either.

Intermediary exchange is only viable once the pool of social relations grows beyond a certain bounds.

The function of my acceptance of any system is the fulfillment of my needs, to some degree. In such a scenario, the only way those needs can be serviced is an equivalence of exchange. In this case, food is required for immediate survival, the tools of procuring such, and shelter, etc. Intermediaries, in such a scenario, provide no guarantee to provide such. So such must be acquired directly. I can eat beans. To take the gold assumes, incorrectly, I can obtain another can or equivalent. That incorrect assumption is a holdover from the fundamental and all-pervasive faith we are at present steeped in and that must be maintained for our reality to function.

It's post apocalypse - you trade whatever you find. The most important commodities will be food, water, medicine. Gold would be practically worthless - it's not going to help anyone survive.