Lucky Strike, only available in larger supermarket chains in my area, but I try and buy them if I see them, or stock up when I am over on the continent...the Tabaconist at Alexanderplatz Bahnhof in Berlin was very helpful in stocking me up

Even had the sterotype paper packets you see in films
Mountain Dew was available for a short time in the UK, a US flatmate had a 'care-package sent over' Hersheys, Mountain dew, Fluff Marshmallow spread (thats was awesome) and just random american candies. Nice to try different things.
The Reeses Cups and peanut butter things are quite popular over here too.
Gaz