Copper is better bought as wire, pipes, square and T joints and other such hardware. Also as water bottles (It kills bacteria, as does silver, takes a few hours tho)
Gold can be used in amalgam with other metals for fillings.
Mercury can be used to make mercury salts (fulminant, for det. caps), also field expedient medicine for syphilis.
Silver and Gold will buy you stuff at inflated prices, and also mark you as a target for looters.
Only point of buying precious metals is for a store of value against inflation, or colapse of monetary system.
So trading them back to money after the shitshow is over, or taking them with you when you flee to another country with different money.
If you are going to remain, after you have bought all your preps, including building several bunkers and stocking them, then you may consider puting the rest of your amazingly large fortune into precious metals, to be traded back into money after the crisis is well and truly over.