"If you want to make money,..."
No, not looking to make money - just a SHTF emergency stash - paper wouldn't be worth squat - ammo, water, and food are essentials for stockpiling, but would need something for barter - hence the silver coins, but don't want to "buy high" even it's just for sitting on.
The next "good" metal in which to invest? Well, I buy .22 ammo in 550 round boxes every time I get a chance... Besides its usefulness on small game it carries good barter value and is a small enough "denomination" that you do not have to give more value than you should for a required item. When they see me at the ammo counter at Wally World, they know that I want at least 4 of the 550 round boxes. They are then brought home, vacuum sealed, and stored away for future trade/use.
Regards,
Raven6