I disagree. I don't think planning ahead is strictly a "first world" consideration. Actually it's more important in an agrarian society, not less, for precisely the reason you're suggesting. Sure if you wait until the food runs out before doing anything about it then it's probably too late. But whether you get it from Safeway, a medieval farmer's market, or you grow it yourself, the trick is to stock enough to last until the next harvest or shopping trip or raid.
You missed the point it's not about planning or stocking. The characteristic time of starvation is days, while the characteristic time of harvest is weeks. While this is the case, food inertia will always be slow relative to starvation. Confer first world, where characteristic time of food supply is minutes. In the former case the food market will be very inelastic and hoardish because fluctuations in demand must be responded to by an approximately static supply.
