I am eating up your responses, all of them, no pun intended :-))
One of the reasons I asked for your input, is that I suffered from quite a few surprises myself when I first came to Amerika.
Kaarina already mentioned the infamous Tuna Sandwich, which is most certainly on top of my list too ;-)
In the beginning, I suffered from severe Bread Withdrawal, that was a really tough one for me!
By now, one can buy pretty decent bread in the USA, be that Italian or French, or whole grain, but in 1984, when I first landed on your shores, it was Wonder Bread - or as I referred to it: Gummibrot (rubber bread), and it was TRAUMATIC. ;-))
The other thing I really was struck by, is the fundamental difference in our food CULTURES, not so much individual dishes.
In the US everything has to be very, very dead. Very, very sanitary. Very, very well packaged. Very, very removed from its initial state of being.
In Europe, it's the total opposite: food has to, preferably, still be alive, smelly and seasonal.
Europeans use every part of an animal or plant, hence the many dishes with organ meats, much like it is in your North American Indian cultures.
Here, food is sensual. The modern markets are but an outgrowth of the ancient ones. The more blood is dripping from the ware, the more earth clings to it, the more fur adheres to it, the better.
Here, butchers still hang carcasses in the window, especially hare with tail and paws attached, to prove that it is not cat.
Here you still will find meats made of horse meat. Not because horses have a lesser value than in the US, au contraire! Waste not, want not. Honor what nourishes you, honor what you took from your surroundings, be it a fish or a carrot.
I know this can be shocking to Americans. But we still have a relationship with our food here.
Food is tied totally to history and locality, hence the huge regional differences, only kilometers apart.