Aside from precious metals, one possible option at least for the short term might be to hold some foreign currencies. Historically, for example, the Swiss Franc was a pretty safe bet in times of inflation and trouble. (See
this research for example.) There might be other clever ways to diversify a bit in terms of currencies.
I think it's important to keep different realistic scenarios in mind, it's not "all normal" vs. "apocalypse". For example, one scenario might be a hyperinflation of the dollar/Euro, and then it might come in handy to have some foreign currencies which you can convert to dollar/Euro as needed to pay bills. Another scenario that has played out in Germany during the recent flood was that electronic payments went down, so the only people who could still buy things in the few shops that were open were those who had some cash. So that's another smart thing: just have a k or 2 of cash somewhere in the house... Comes in handy in daily life as well.
I'm not sure that a pile of ammo is gonna save the day; or any other tangible good that we
think might be in short supply during a crisis. These sorts of things are kind of unpredictable (toilet paper!). Maybe our best bet is to stockpile stuff that we
actually need, and can use
right now, instead of anticipating scenarios that may or may not play out.
Just some thoughts. I personally have still lots of homework to do on the prepping front.