I bring back usually from M&S: shortbread/biscuits, Christmas Cake, Mince Pies (though this time for Thanksgiving I brought back jars of homemade mincemeat- my Mom said it was the best mincemeat she's ever had

), Percy Pigs/Colin Caterpillar
I also like to bring Jelly Babies, sweeties like Parma Violets/Love Hearts, UK Smarties (even though I think they're gross), Kinder Surprises, Kinder Hippos, Penguin bars
Mr Kipling- bakewell tarts, blackcurrant pies, etc- people love Mr. Kipling!
Jars of locally made chutneys, jams, mustard, pickles
Whisky or Ciders or Beers that you can't find in the US (this takes some searching as tons of stuff is imported to the USA)
Teas- PG tips, Twingings
Fortum and Mason things
Have fun, I love to bring food gifts!