My DP's parents are from England and these are the things they always bring back with them:
Seville orange marmalade
mint sauce
Bisto gravy granules
some Home & garden magazines
They also buy fresh things at a local British shop (the British Pantry, it's called) like sausages, cheeses and puddings at Christmastime, and there are some mail order companies as well. They get things like Branston pickle and HP sauce at the shop as well.
Me personally, I really miss (from the UK) Kettle Chips Sea Salt and Balsamic Vinegar flavor. Also Fox's Crunch Creams and PG Tips tea although sometimes I can find these things at Cost Plus/World Market. I also REALLY REALLY MISS jars of curry sauce, Korma in particular, there are lots of good curry sauces in jars here but nothing compares to the jarred Korma froM England. I usually have my friend send it to me or bring some back when she comes for a visit

I belong to another forum with US expats living in the UK, and some have repatted to the US (like me) and we are having this same discussin at the moment... here are some of the things they bring back to the US from the UK:
crumpets, Remegel, Yorkie Bars, Warburtons Super Toastie bread, Thornton's toffee,
Orange kit kats, any and all kinds of chocolate
Christmas crackers, interesting flavors of crisps, Prawn cocktail crisps, Robertson's mincemeat, Carex Liquid soap, mini-mince pies, flavored crisps, magazines--usually BBC History, McVities Milk chocolate digestives
,Cadbury fingers,
Lemon fanta, Yorkie bars, Flake bars, Charlie and Lola magazine ,Cadbury Creme egg bars, And of course Tiptree jam for everyone!
Chocolate Hob Nobs, Smarties and Fox's Biscuit Assortment, Tinned mushy peas, Teacakes, Hendersons Relish, Marmite, Irish Cream Chocolates, Twiglets, Spotted Dick
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