There is a lot of government and academic research done into how people behave in a disaster and it's not how many imagine.
I'm all for academic research, unless it doesn't stack up against what has actually happened in the real world. Many will work together. Many will not. If you think everyone is going to rally together you may want to talk to the victims that were in the Super Dome during Katrina. Or perhaps talk with the first responders who were fired on while trying performing rescue operations. Or talk to the police from that area...I'm mean the one's that weren't actively looting themselves.
So yes, many folks will band together and help each other. Many are going to panic when they don't have food and water and their way of normalcy has disappeared.
Better to have prepared ahead of time. That's just common sense.