When I was challenged as to what I would bring with me if I knew I were going to be dropped into a human civilization at a truly random time and place, if I wanted to be sure I had something that would be valued by the society I landed in, I answered, not-so-jokingly, "Salt and pepper." This has gotten me on a not-yet-successful quest to find long-term data for the real value of salt.
I did find values
from 1900 to the present, and they show something interesting. I saw this on the web
here literally minutes before I was about to plot it myself. I'm going to show my own plot anyway, just to show that I verified the data. I still have not found out how to make Excel plot a decent log scale, so my apologies for that. There are two points I want to make. I have data only for the first, but the second is more important.
The first point is from 1900 to the present,
the real value of salt has been much more stable than that of gold. Gold has, of course, been a much better buy if you bought it at the right time--and a much worse buy if you bought it at the wrong time.

The second point is the one for which I don't have data. It is that salt was awfully valuable for a very long time, and then became so much cheaper that the idea of salt as valuable now seems like a joke.
The obvious riposte to the idea of salt as a store of value is that it is not worth enough.
But cheap salt is a very recent phenomenon. For
millennia it was a prized and expensive luxury. Salt cellars were made of gold because the valuable salt
deserved to be displayed ostentatiously, and simply having an open container of salt on the table was a status symbol. Salt has had at least as much mystique surrounding it as gold, and we are paid a salary, not an aurary.

I'd love to know how the value of the salt in a salt cellar compared with the value of the gold in its container. Yes, I'm sure that the gold was worth much more, but I'm equally sure that portable quantities of salt were valuable enough to be a practical medium of exchange. Whether the value of salt was as stable over the millennia before 1900 as in the century afterward would be nice to know.
If you dropped me into a time-and-space-machine to emerge at a random society in human history with as much salt and pepper as I could carry on me, I'd be OK any time up to, I don't know, I'm thinking maybe 1700. Obviously after 1900 I'd be in deep trouble.
And that's the point. One can imagine a 16th-century saltbug making a good case for the special characteristics, universality, and long-term safety of investments in salt. But something
can be universally and cross-culturally valuable in time and space for centuries and centuries--and then become so cheap they dump it out of trucks onto the roads in wintertime.
Annual income twenty pounds, annual expenditure nineteen nineteen and six, result happiness; Annual income twenty pounds, annual expenditure twenty pounds ought and six, result misery.