I agree the delusional fantasies many have here about PMs becoming the currency of the apocalypse is ridiculous though. The currency in that scenario would be 100% hard goods or services like EW mentioned. I also think the same posters who fantasize about the complete end of the “grid” will be disappointed. Most craphole third world countries have internet, cell phones, and power...even if they don’t have clean water or abundance of food.
There's many sorts of SHTF events. Everything from an EMP or nuke attack, to generalized famine or another release of a lab virus...this time, maybe, more successful, from TPTB's standpoint.
We may or may not have the grid. If we have devastating famine; or invasion by a hostile power here to loot...the grid ain't staying up. Because it needs men and equipment and supplies and paying customers, to stay up.
But, to your point: Yes, when in an EOTWAWKI event, gold will be useless. Silver will have some utility but not greatly so. As you say, barter will be the rule of the day. Commodities will be food, liquor, salt, spices...services, skilled or mercenary. Sex. Yes, it will be ugly.
That's in the chaos. Chaos won't last long. CANNOT last long. If it lasts, if it is deliberately prolonged, then...all fall down. Dead.
Because chaos is unsustainable.
Gold and silver are for AFTERWARDS. When order and local civilization re-emerges. Trade is the natural activity of Man; and bartering milk or picked crops for other needs, doesn't work well. What if the tailor or cobbler has a cow? He doesn't want your milk. You have to find a "buyer" in a day or so, or it becomes waste.
Precious metals are...money. Money is a placeholder. Money is what you offer for what others have, that they can take to offer for what they need that still others have. It eliminates the awkwardness and spoilage of barter.
Dollars and bitcoin won't do it.