I have a few friends who buy gold coins thinking that they're a hedge against doomsday. I always ask them what restaurants will acept them as payment? And furthermore, what do expect in the way of change? Gold shavings? Silver dust?
All currencies are based on faith. What makes gold valuable or any more so than sea shells? Nothing but general concensus.
Gold will always have a value since it is in high demand for jewelry (and other applications) and it is very rare, if "doomsday" does it, it would raise in value by around a thousand times, however if it doesn't come, it will decline in value considerably from what it is now. The reason why "currency" has no value is because it is printed on paper in the form of notes, the paper is relatively worthless. If the "shit" really did "hit the fan" then you would actually have your precious metals weighed off into small increments which would be sell-able and have an established value. It could be solid, dust, shavings, just don't loose it lol...
I'm sure a business would pop up that would melt the impurities from your gold or silver away and then put them into tiny coins or bars for you with a marking for a fee so you could use it for purchases, although more than likely there will simply be a bank that deals in precious metals and will issue paper notes for your precious metals. As long as they don't carry too much debt, it works (run on the bank).
The problem with buying gold coins is a lot of the value isn't the gold, but it is the design of the coin itself (which no-one will pay extra for) their actual value in pure gold is far less than what people pay. The best way to buy gold is more likely to buy it in plain bars from a distributor (which probably requires a significant investment). They will likely charge you around a 20% commission.