That’s… not how currency works. It has to be assigned a value and there has to be some consensus about it.
If I take your gold for my weapons and food, but can’t buy stuff with it because someone states that they don’t want useless gold for exchange, I probably starve to death. Therefore, I don’t accept gold in the first place to don’t risk anything, which will devalue gold.
Here’s a good read on the value of gold to acient native americans, although I can’t confirm the quality or accuracy of it.
Well, if you explain to me how they would be able to tell if it’s fake gold or not, I would be a little more convinced than now.
You can see how some people react to a crisis right now - and you really think they would be honest and fair in an apocalypse? Well, probably some, but certainly not all.
Yes, all goods can be counterfeit. I did not state otherwise in my answer. I just objected your statement, that gold can’t be faked.
Also, I can open up a can and just take a sip from it or open/testfire a bullet. I can’t do that with gold.
It’s funny, I actually have written up a “Of course it can be used as a firestarter, which would assign some value to it as a material.”, but deleted it, as I wanted to keep it simple.
And I’m sure I wont give you 10 breads for a 5 $ bill to start a fire.
Gold can be used as a shotgun ammunition and a conductor. And to weigh down your dollar bills tinder so it doesn’t fly away. So it’s not totally worthless 
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