My wife and I call these "triangle sandwiches" and crave them often while outside the UK.
Much better than the over-processed absolute junk you find in refrigerators at gas stations in Canada and the US.
Supermarkets (hm, deja vu) also tend to be much more heavily stocked with "walk out and have supper" food which the Canadians just don't do.
I did come across a Pret a Manger in NYC yesterday which is exactly the same sort of stuff as what Ken is describing, sandwich wise. They are a big chain in the UK, only exist in NYC in NA and HKG in Asia.
Simon