This is great! Now I've got a bunch of people to disagree with...

Whole Foods is a good store but it's not a supermarket, not like the national chains we're comparing.
Trader Joes??? They have some good stuff, granted, but better than a Waitrose? No way. Not even close to a Tesco!
My last time at Trader Joe's in San Diego I heard a woman tell her friend: "Look at all these cheeses!" I wanted to laugh. There was your usual cheddar and Monterey Jack, plus a couple Bries and Camembert. Even Tesco (no, even Lidl) has so many more varieties.
In fact, the range of choice in a British supermarket can be downright overwhelming. It's a good thing the quality usually matches the variety.
Ready meals? Anything like M&S foods in America? (although I do have a soft spot for the Swanson's Big Boy mexican meal!).
I have to agree with you about the expensive produce. It can be shocking. I mean in the San Diego supermarkets flimsy tomatoes were priced at $1 EACH! Similar prices for lettuce and other produce. And California is called the salad bowl of America.
Fast food is the only thing in the culinary field that's better in America. And Chinese restaurant food. In every country I've been to Chinese food is different but the way they do it in America (at least in California) is great. The British ones just don't have it quite right.
Also, takeaway pizza chains are better (and much cheaper) in the U.S. But supermarket pizzas from the U.K. are way better. American store pizzas have some weird metallic aftertaste... must be all the chemicals.
Luckily, Indian food makes up for the lack/lower quality of other fast food in Britain!