Peter, can I assume you are european, perhaps more specifically english?
You continue to make some of the same points I see made in other places by europeans who don't quite "get it".
First, many Americans do not drive "big" vehicles just because they feel like it. I own a minivan because I have 3 children and a dog. My next door neighbor owns a large pickup so he can tow his lawn service equipment. My father in law owns a monster SUV because he runs a boatyard and he needs to have the ability to tow boats around. My father owns an SUV because he works at said yard and needs the ability to tow boats and move tools (arc welding equipment, etc). I own a pickup because I do all my own work. When I needed shelves in my garage, I purchased lumber and built them. When I wanted to landscape my house, I purchased the material and brought it home. When my tractor or other equipment breaks, I need a way to get it to the repair shop. That's how I can afford things - by doing them myself. That's somewhat of a theme here in the US (outside of the big cities). Small or family own businesses are huge in the United States too. Huge. Construction, landscaping, etc being probably the biggest in my area.
Now on to to this whole shopping thing. In the US, shopping is not a 20 minute walk-in-walk out thing. Just standing in the lines themselves will take you 15 - 30 minutes. Grocery stores are generally 20-30 minutes away. And shopping for a family of 5? When you start going through a gallon of milk and a loaf of bread a day, two bags of groceries would become an everyday thing for most American families if they shopped in the manner you're talking about. Are you single as well? I can't see anyone with an average size family who would say they could go get two bags of groceries a week and be done with it. It doesn't work that way.
Believe it or not, the majority of Americans still live in Rural locals. Unlike Europe, England, etc, where the majority of people live in cities. Land in the US is still quite abundant and still quite cheap: my friends from Europe were flabbergasted when they saw the house and lot I own on a very small salary.
As such, blanket statements like you're making don't fit. Mass transit has been worked on for decades in a major city (+1 million population) that I live near. However, it just doesn't work because the majority of people don't live in houses jam packed side by side. When you start talking about 2+ hour commutes on buses and exhorbitant charges to maintain the system, it just doesn't work.
I do not ride a bus because there are not buses near where I live. Yet, I live 10 minutes from my job (8 miles).
Many of the basic things that allow high density populations to live in the manner you're suggesting simply are not present in the United States, and probably will not be for another couple hundred years.
That isn't to say that any Americans aren't wasteful - many are disgustingly so. Nor does it mean that all Americans wouldn't benefit from mass transit. In the places where it makes financial sense, it has been done - New York, L.A., San Fran.
Some ideas - like raising the taxes on gasoline, would help drive less consumption. We're already beginning to see a major shift in purchasing of vehicles here in the US. There are already additional taxes on larger vehicles as well.
When people talk about consumption and resources in the US, they have to realize that the only thing that will drive savings is an increase in cost. And our government, and our people, will never support the social engineering required to do so through taxation. Perhaps that is selfish - but you know what they say about people who live in glass houses.