But New Yorkers tend to carry their groceries home in their hands for as far as a mile, instead of wheeling them out in carts to a car trunk and then carrying them 20 feet to the door of the house.
Heavy items (liquids and canned goods and stuff like potatoes) WILL tear through plastic bags if not double bagged. The worst offenders are half gallons of milk/juice, which have sharp corners.
This has happened to me more than once. I've also on occasion just made it home with a bag that's seconds from splitting open.
And then you're half a mile from home with your groceries all over the sidewalk and nothing to put them in.