Were you possibly referring to "The Trigger Effect"? This is worth
renting, simply for the psychological aspects.

I have been in a modest "Blackout" that encompassed
about 40 square blocks in a downtown area. Just about
this time of year, too.
Fortunately for us, we had water. But there wasno AC;
no lights and no refrigeration. The McDonald's franchise
a few blocks away cleared out it's supply of Egg McMuffins
within an hour.
Police for security were nearly unavailable. There was an actual bidding war presided over by the Police Guild for latecomer businesses.
People's reactions were fascinating. For the first 24-36 hrs,
they treated the event like a party-everyone pitching in to
help. But then, composures started to fray and tempers became real short. I remember an incident over a razor and
another over spilled ice cubes.
The Red Cross provided "survival rations" consisting of
stale coffee and those very same egg mcmuffins I mentioned.
Fortunately for us, the police department flooded the area
with "Blue" so really violent incidents were almost non-existent.
But, I DID surprise two solid citizens busily removing money from a parking lot cashbox. It gets DARK in the city when
the lights go out. Coincidentally, I was dressed in dark blue and the would-be crooks apparently thought I was a cop.

My advice? Keep a good solid D-Cell Maglite or one of those
lights that use the big 6 volt batteries;PLENTY of extra batteries-we couldnt even watch ourselves on TV; maybe a suspicious dog with a good sense of smell and get to know your neighbors.
We had people congregating at all hours at the entrance to
the hotel where I worked. Most comforting when it's DARK out. I'm talking so dark that you can't see across the street.

Shotguns are intimidating but a good semi-auto pistol and a
reliable flashlight (not to mention a loyal mouthful of sharp teeth) might help you as much or more.

If you choose to keep a weapon, learn to use it well and practice,practice practice. WAY too many folks think they can treat guns like insurance policies or protective amulets rather than as using tools.