First and most importantly: Jaffa Cakes. The best I can figure is that one of the ingredients is crack cocaine, as it seems to be impossible to leave a package unfinished. (And they’re cakes, dammit!)
“Jaffa”, for our US audience, is a term for a seedless orange. And occasionally a derogatory term for an infertile man (from the “seedless” connotation). Which makes watching “Stargate SG1” unintentionally amusing at times.
Next: biscuits. Not only does the British term “biscuits” encompass an assortment of cookie and cookie-like products, plus dry crackery things (sometimes labelled “Biscuits for Cheese”), but also (sometimes) includes candy/chocolate bars which have baked interiors. Which means that in some supermarkets KitKat and Twix bars (“chocolate biscuits”) are in a different aisle than, say, Mars bars. Very weird.
What the British call “crackers” are paper tubes filled with cheap toys, paper hats, bad jokes, and a small explosive charge which two people pull apart (like a wishbone) at Christmas dinner. These are not edible, I hasten to add.
Crumpets are like English muffins, only squishier. You can buy both in many supermarkets.
Trying to explain to a British person what “pudding” is in America (“It’s sort of like a firmer custard, but in different flavors…or like a thicker mousse…”) is like trying to explain the game of cricket to an American. Some things are just too foreign to comprehend.
On that note: any food product prefaced with the name of a foreign country will bear no relation to any foodstuff available in that country, unless they’ve been imported there from elsewhere. So none of the various products labelled “American” or “American-style” in British stores are available in American, or even palatable to most Americans.
[rant]
There is a special circle in culinary hell for the person who invented “American Ginger Ale”. Who thought that putting sugar, saccherine AND aspertame in the same product was a good idea?
[/rant]
And finally: if OED English = British English, how come the OED prefers -ize word endings to -ise?