Let's say that the economy really did collapse and paper money became worthless overnight.
Do these people really think that they can grab a gold bar out of their safe, head on over to the supermarket, load their carriage full of food and then slam a gold bar on the counter to pay for it?
How would they get their change?
Most likely by the time the fellow got home got his gold bar and got back to the supermarket the point would be moot being the people who didn't have any gold would have stormed the supermarket and took everything because their welfare/debit cards didn't work.
And in such a scenario if there was food still left and he showed his gold bar to pay for his food he better be "well-armed" because if not he won't be "well-heeled" for long...
No, I don't think anyone believes that.
If they are rich enough to have enough gold at home to "slam" on a grocery counter then they will be smart enough to take their "bar" and use it to make a long term contract with a party that can supply the needs they seek over a long period of time.