Never. I assume we either all make it by helping each other or we don't. So there is no reason to prep. My prepping is looking for ways to create as much progress as possible and doing anything else feels regressive to me.
How will you help other people if the economy breaks down?
When has the economy ever "broken down"?
Great Depression? Every war torn area ever? Shifting markets causing ghost towns? Every large emigration such as the Irish Potato Famine? And then you have “so dysfunctional that it may a well be broken” economies. See life in slums or very poor regions.