I stayed with a friend who lived in London and walked to work through a commercial area; buying something like a jar of jam just meant stepping into a store she was walking past anyway. As easy as someone picking up a coffee or a sandwich every day for lunch.
Of course, shopping in convenience stores is expensive - but everything is in London.
Meat and fish, greens, and some vegetables plus whatever odds and ends I ran out of since my last larger grocery run.
Generally this means I’m never out of anything, my food is as fresh as the grocery store’s and/or the farmers’ markets, and I buy only what I need and will use in a dish within 48-72 hours.
Certain things, spices, a few different “safe” cheeses, and anything that I buy in a can or a jar tend to get picked up in one large shopping trip every two or three weeks, but also restocked in my daily grocery run on an as needed basis.
Of course, shopping in convenience stores is expensive - but everything is in London.