This is a common belief, but I don't subscribe to it. There will always be those with more than they can consume/use. They don't need more food. It will just spoil. Some believe only land will be valuable, but land needs to be defended, and there is a limited number of people anyone can trust.

So even if it really got to this level of SHTF (which I think is unlikely), there will still be someone who is wealthy willing to trade excess food or land for gold....or weapons. Shiny rocks don't expire, and are relatively easy to protect. There will be a market. It won't be me making that market, but I'm sure there is someone out there who is beyond self sufficient and ready to take advantage of that.