Sri Lankan here. I personally experienced this last year and was very surprised. We Sri Lankans love to criticise ourselves for our wonky moral compasses, so when the early protests started, I stocked up on food and installed an extra CCTV camera, expecting widespread riots and looting. They never came. There were many organised protests, and protesters did clash with riot police around government buildings, but people overall were unusually helpful toward each other.
Several times, I had taxi drivers refuse to accept fare when they picked me up from a bus stop late at night (both petrol/gasoline and buses were in short supply for a while). Once a motorcyclist literally stopped by and handed me his spare helmet saying "If you're heading my way, I can take you". Many people (including my wife and I) drove around distributing food and supplies to folks we felt were in need. It's hard to describe what came over us, but it seemed like a common phenomenon that affected a lot of people.
I still think if food became really scarce, selfish, violent behaviour would have emerged. But fortunately it never came to that and the country managed to go into a debt restructuring program with the IMF.