But are the places you’re eating 1) fairly affordable and 2) quick / fast food and not a proper sit down restaurant?

I had an extremely difficult time finding places with those requirements. Everything seemed to require sitting down for at least 20-30 minutes, which didn’t fit my walking schedule.

I didn’t have the same problem in NYC or Paris, where it’s very easy to find a variety of places to grab a kebab, baguette sandwich, pizza slice, dumplings, etc.

Yeah definitely affordable and quick. And can get all of those in London with zero effort. Most of the time I just search for food on Google Maps and pick something which doesn't look poisonous.

For example, going here tomorrow at lunch time https://www.southbankcentre.co.uk/food-and-drink/southbank-c... - will work out what I'll eat when I get there.