The fragility isn't necessarily in the availability of food. It's the vast transportation network that runs it (all depended on oil). If everyone was getting food from a local farmer, then there would be zero cause for concern. I'm not saying mediums of exchange are worthless, I'm merely pointing out how fragile our current system is for meeting needs as vital as food!
Suggesting we design systems that are not dependent on mediums of exchange (and vast fragile networks) for meeting our basic needs. And delegating these mediums for helping us meet our wants and nothing more.
All the while decoupling mediums of exchanges with stores of value...
Simple things ;)