As someone from the UK, I don't know the cultural significance of Hersheys. I've had Hersheys chocolate a grand total of two times and frankly it was not very nice. Is it prolific in the way that Cadburys is here? Can you get Cadburys over there?
More importantly do you see Green & Blacks (or similar brands) in almost every shop?
Also, Smarties are way nicer than plain M&Ms IMO, but I love me some peanut M&Ms. Most of the products talked about in the thread (Smarties (UK), Aero, Coffee Crisp etc) are Nestle products which is interesting, such a big multinational having such specific products per country.