I think versions of this anarchy could explode in many large US cities if the power and water were disrupted for even one week.
Sadly.
A week might be optimistic.
large swaths of most large US cities are already very unsafe for some folks to travel through
No doubt about it. The lesson that should be taken to heart is that when the SHTF, what you need just to survive will not be available on any shelf in a very short period of time.
The run on gasoline in San Antonio and the surrounding areas was initially driven, I suspect, by the fear of a price hike. That's all it took to create a temporary shortage, everybody just topping off their tank.
That doesn't explain the run on other items though. People were stocking up on bottled water, eggs, milk, bread, and canned goods. Batteries were a hot item too, especially D cells common to most flashlights. Whole sections of shelves were cleaned out at our local grocery store. The cashier said they had just gotten in some bread and eggs when I went in on Thursday, but that was about it. If you were looking for those other items, you were SOL.