FWIW, I brought back a load of candy from the US recently to take into the office for
British people - they quickly gobbled up all the following:
Mini Reeses Peanut Butter Cups (regular size are available in normal shops here, yes - but I've never seen the minis)
Jolly Ranchers - the individually wrapped bite size candies (the Brits have told me that Jolly Ranchers
were once available in the UK - maybe like 10 years ago, but then they disappeared from the store shelves, never to be seen again)
Tootsie Pops
They enjoyed the candy corn and 'Autumn Mix' (candy corn + mellowcream pumpkins) as a Halloween oddity - but didn't gobble these up as much as the above. Brits tell me candy corn tastes 'like fudge'.
There are still lots of Tootsie Rolls left, so they didn't go over quite as well.
Also, I brought back peanut butter cream-filled Oreos & the Brits were really surprised that all of the different Oreo varieties (peanut butter, mint, berry, etc) aren't available here - just the regular & the double stuff (I think?).
As for Americans, I know people who are jonesing for Cheezits - there are like a milliion different varieties of Cheezits now in the US - who knew?!
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I always miss the Triscuits (in various flavours) & graham crackers.