Most of what I cook comes from four places within ten minutes of the flat, and one of them is a supermarket.
Worth walking for
Eggs from the stall by the old fish market, because they are two days old rather than two weeks. Carrots with the tops still on, from the woman who thinks it is strange that I want them. Bread flour from the shop that sells it by the kilo out of a sack.
Not worth walking for
Onions. Tinned tomatoes. Dried beans, unless you want the big flat ones, in which case walk. Butter, and I say that as someone who gets through two blocks a week.
The rest of it is a supermarket and a bit of reading of labels, and anyone who tells you otherwise is selling something.