The supermarket is a direct result of car culture. The supermarket did not come first. You buy your week's food in some nations, you know, during the week, when you are going to eat it. From a store around the corner from your residence. This model makes much more sense sustainably - smaller, local businesses (owned by the people who live around you) are supported, food does not need to have billions of preservatives, and you get fresher food. As someone who likes to cook, I think you would be all about this.
That you do all of your shopping once every week sounds like madness - not just on your part, but on the part of the stores which are designed for people to do just this.
I've been biking to work and stores for a couple years now, and it works out just fine for me - I take a large backpack and can fit at least 3 days of food in it - even including the massive amounts of wine I drink. When going to work I can easily fit bike gear, folders, a laptop, and a change of clothes in too. Lunch maybe, but I've never tried. In any case, I'm just saying that if you wanted to, it would be completely doable by just adopting more community-based habits. (assuming you live in a very urban environment here, or europe)
I doubt a better nationwide rail system will help this much, but at least it's a step in the right direction. maybe if the government provided more aid to city-wide transit, we'd be getting somewhere.
