Historically, governments would operate grains silos and be an intermediate purchaser, to control the cost of grain - keep it slightly higher in good years, and keep it stable in bad years by dipping into reserves.

IIRC a lot of countries were forced to abolish these price controls by the WTO, and then were screwed over when they got a bad harvest and poor people had no food.

That's an interesting question: how much would it cost to keep 3 years of food (let's assume the bare minimum - refined white flour) in reserve for the entire United States? What is the cost of food subsidies over the same period?

There’s some issue with storage - long term storage of food leads to the nutrients decaying.

Solution: rotation system.

I think India does this and has been doing it since WWII under “public distribution system”