Looooooongstanding Store of Value
Gold and silver have a history as a store of value that can be measured in millennia. Yes, it is a convention, but a convention so powerful and longstanding that it has become a useful assumption. We can assume the pull of gold on man as we can assume the pull of gravity.
Gold is money
I like owning productive land and operating businesses too, but it is also nice to have a store of value that is unchanging. I do not think of the value of gold and silver as denominated in US$ or any other fiat currency; instead I think of the value of gold as denominated in gold. Neither its supply nor its demand changes much over the scope of time that is relevant to me. One can deny that gold is money, but if gold isn't money, then nothing is. I would submit that it holds more of the qualities of money as historically and properly understood than any widespread paper currency in circulation today.
Systemic Insurance
I could be justly accused of being so safety conscious that I am on one side or the other of paranoia. I take dramatically elaborate measures to maximize financial and physical security. I rather enjoy the topic, so there is little downside, but I assume away very bad things happening, prepare for them, and then anything else is just upside to enjoy. To that end, there are many things that can be insured against. However, there is not particular way to buy systemic insurance via financial instruments. If our integrated, complex, tightly coupled modern world breaks down - even for a short period of time - one may want systemic insurance.
Is it really necessary?
I think that the best way to think about it is that dozens of preeminent civilizations have crashed throughout human history and it was almost always fast and almost always unexpected. While there were no opinion polls at the time, my sense is that few members of previous hegemons would have expected their demise. But that does not stop the demise and such a demise looks like a multigenerational decline in wealth, security, and technology. For the most part, no one expected it and no one was prepared.
This time it is different - we are in a New Era
Following the Spanish Influenza pandemic and World War II, western civilization has been in a golden era without events that have revealed systemic vulnerabilities by wiping out major swaths of populations. This has a superficial as well as a more substantive impact on our thinking about our system's weaknesses. Superficially, it has worked so far and so the appearance of stability has lulled people into a sense of complacency. More substantively, it has leached from modern society all of the skills and the stuff necessary for a basic level of survival in any environment but the one we have recently created.
We are the living in the least adaptable, most evolutionarily precarious civilization ever. If things went horribly wrong, American frontiersmen in the late 1800s were perfectly acquainted with the skill and the use of the technology of earlier civilizations.
If necessary, they would be perfectly passable Iron Age workers.
Likewise, you could toss an Iron Age worker into the Bronze Age or even the Stone Age without causing too much trouble. Such a technological retracement would elicit a few shrugs before they got back to work.
But if their technology was turned off, what on Earth would these guys do?
If we were forced to lose our most recent and most tightly coupled technology even for a few short years, we would not be able to smoothly transition to an earlier technological level - we don't have the skills and we don't have the stuff. On average, we have fewer of the practical skills that our grandparents had than any previous known generation. At the same time, we require all of our most advanced infrastructure and logistics to support our current population density. That density would decline precipitously in a matter of months (and this would not be the ideal way to solve the problem).
Precisely when it is most countercultural and most variant is when it is most relevant to have contingency plans for systemic risk. I think that it is sensible for professional people to know at least one trade skill in case their chosen profession becomes obsolete and irrelevant. Even with a trade, it is sensible to know enough primitive skills to be able to survive civilization-level retrenchment. And finally, it is sensible to have a means of trade and store of value. The means of trade and store of value that have bridged prior hegemonic collapse have been gold and silver.