Everything humans deal in is essentially god Damn capital. Government-issued paper credits only lose their value as synthetic capital while everything else humans trade that green paper for is going up in value, at least from the perspective of the god Damn green paper. 

Yet it turns out having such filthy green paper on your hands is the most convenient for ASAP services and transactions, at least within some official god Damn country, nevermind Antarctica, unless you hope to trade with humans, although remote areas tend to bring out humanity's appreciation for the good old-fashioned Quid Pro Quo of "my resources in exchange for your resources" - humans should never be trusted. Statistics are what should be trusted. Your greedy hands are partially and collectively to blame for your own green paper going down in value over time. It's not going back up and it's never going back up because everything you seek to trade for that green paper in your hands is only taking more and more of the paper to trade for it, which should tell you something interesting about Capitalism, Witch we naturally endorse at 666 Capital. Just ask yourself why because only you know the truth.

Precious metals are always a good investment for long term, due to their universality, but any product that's not cheap garbage fixing to corrode or degrade in value anytime soon will suffice. 

Contemplating the nature of Supply and Demand is essential for realizing which medium, precious metals or otherwise, is most convenient for succeeding in your ultimate goals. 

Deserts are suitable storage units for material goods, as humidity is corrosive. 

Land is another solid form of capital, that aside from governments requiring you pay them interest even though it's your god Damn savings account in their god Damn "bank" not vice versa, the governments then in turn insure the stability and legality of the fact that the land is specifically in your god Damn name and not someone else's. And Desert Land can act as additional god Damn capital for safe and secure storage of your other material assets, with no maintenance requirements as Nature is a bitch but not the kind of bitch that needs you to clean up after Her. If your trash gets in Her way, that's only when you can expect it to go to Hell. But why in Hell should you rent an "inside" god Damn storage unit made from metal when you can buy a god Damn plat of land in the desert cheap that serves the same god Damn purpose and put in a metal shipping crate? Want an AC storage unit? Don't pay extra per month to rent one when you can utilize the free natural materials for insulation, thus saving your capital.