You don't have to go every day. You can also take a hand cart if you really want to stock up. It's also just much less of an ordeal to walk down the street and grab some things than it is to deal with the car, traffic, parking, gas.

You have to go outside in the cold weather when you drive, too. Plus you're more likely to get in an accident if it's very rainy or icy. Not a compelling argument.

Foot traffic is also better for the neighborhood in terms of economic and social health (see: Death & Life of Great American Cities, by Jane Jacobs).

I live within walking distance of several large supermarkets, in addition to bodegas and smaller groceries. I don't live in a fancy or expensive neighborhood. I don't know why you think that there would only be expensive places near where people live.

Also even if it was spending more money on food because you only live next to an expensive bodega, you're ignoring the huge externalized costs of car-first culture. Pollution, pedestrian deaths, opportunity cost from lack of walking, economic loss from lack of foot traffic, safety loss from lack of foot traffic, and so on.