Gold is potentially useful AFTER things get back together again. If there is a major disaster - US falls apart, as does the rest off the world. 95% of the world population dies, but by luck you are one of the survivors (this luck seems to be a factor most survivalists don't think about). For a few years there is chaos as people try to figure out how to get food without the supply chains in place. (worse in the cities, but even rural areas are dependent on the supply chain for fuel, fertilizer, seed, repair parts, and lots of other things)

After a few years things start to settle down. Trade with your neighbors becomes possible for some division of labor. However trade works better if there is a currency. Paper money is either degraded (the most common bills last a couple years), and the replacements are all obviously bad copies. What is needed is something that is easy to verify, that is hard to copy, has some intrinsic value, isn't so common that you need vast quantities, and something you are willing to trade. There are many choices for this, but gold is one of the better ones. Even if something other than gold is chosen, it is rare enough, and valuable enough (for good looks, and it is somewhat easy to for into useful shapes) so you can expect to find a market for your gold. Many of the things you can choose instead are either useless (computers without the entire power grid can't do anything), or so common that nobody will care (why would I want your iron when there are junk cars everywhere with plenty)

Note that in order for this to work you need to actually have the gold in hand. If you invest in gold without a safe to store it in, then it does you no good. Even if you can get to Fort Knox, whoever is there first won't recognize your claim to the gold inside.

You also need to consider inflation, thousands is a nest egg. millions is more than the local economy needs. People don't need to accept your gold, unless you are the local warlord, and then you don't need gold.