I have thought back to the origins of this need. I grew up in a large family where we all ate meals at a large table made (from my mother's design) from a door. The serving dishes would be set in the middle and passed around. If I was not greedy enough I might not get as much food as I wanted. I always wanted more than I actually had need for, though. Perhaps there is a connection.
By the time I was 12 or 13 I had taken over the grocery shopping and cooking for the family, so I also controlled access to food. It seems like this control should have relieved me somewhat and that certainly by now, when I am the sole controller, I would be able to let go a bit. But I still like to stock up.
I am overweight and in no danger of starving. I have a regular income so I can continue to buy food. This part of the country is not subject to disasters that leave us stranded - like snow storms or floods. Yes, a little flood now and then but never anything that keeps us from moving for long. Yes, there are earthquakes but those don't shut us off either. So there is no logical reason for me to stock up. Perhaps in preparation for some kind of attack? But in that case I'd probably be dead anyway. Or the economy goes bust and there is no food to buy? My stock wouldn't take me all that far in that case.
It perhaps doesn't really matter if there is a logical reason. The only thing that particularly matters is that I not waste what I buy. My record on that score is better than it used to be, thanks in large part to those magic green bags (evert-fresh bags) in which I store fresh vegetables and fruits. There are many times when I have no interest in leaving the house to buy food, so I rummage around and make what I can from what is in here. This may be the main reason I have so much. I can make something edible from almost anything I find in my kitchen, and have been able to for about fifty years.
I have to admit that when I look at that picture and all the meals it represents it makes me feel warm and safe.