First lets start with the obligatory mention that thanks to zoning laws in the US you are even in this predicament. My grocery store is like just a few hundred metres from my apartment and on my way from work. Instead of weekly shopping I just do it daily / every other day with just the few things I need for those few days. No for hauling grocery bags. And like you wouldn't go shopping before appointments either...
Also you completely forget to factor in the cost of owning an maintaining a car. A yearly ticket for public transport for me is around 500€. I don't own a car so my expense on public transport is just that 500€ with a bit more for holiday trips etc compared to the cost of buying a car every X years, paying for maintenance, and for fuel.