I'm not sure I would characterize the relative calm and civility as stoicism. And certainly some suppression goes on as a coping mechanism in an extraordinarily stressful situation.

Not everyone thinks that going into survival mode means you have to step on the person next to you. Especially when you know that there are others who are still in immediate danger or have suffered far worse. So maybe the people who are queuing up for food are grateful to be out of immediate danger and for the companionship and support of the person next to them in line.

I would venture to guess that there is a certain amount of psychological preparedness that exists in Japanese culture, beyond all of the building codes and warning systems and emergency responders. For example, I'm given to understand that kids in Japan do drills on a regular basis on what to do in the event of an earthquake. So it's indoctrinated what to do: how to protect your body while the shaking is going on, when it's safe to move to another location and where the designated safe place is in your community (might even be their school). Maybe if you're brought up with that kind of preparation you are less likely to panic anad become emotional when you are hit with a big seismic event.