By now you've read descriptions and seen pictures of Twinkies. In case you didn't realize it, they are a product of the Hostess company, which makes snack-sized cakes and pies.
Personally, I always preferred Hostess cupcakes, Suzy Q's or HoHos to their Twinkies, but it's Twinkies people mention in the catchphrase about "giving up the Twinkies" (going on a diet).
Growing up in the Midwest, Hostess was THE reigning brand for snack cakes. Others were considered "off-brands" and not as good. Moved to Philadelphia, where Tastykakes were the home brand to find Hostess products dismissed. "They don't have anything like butterscotch krimpets, do they?"
Philadelphia is a city that loves its pretzels. They sell hot, soft salted pretzels from carts on the street, often with mustard, and it's considered perfectly fine to have a pretzel for breakfast.
You know the expression "as American as apple pie?" Apple pie is a classic, but I don't know that it's really all that popular any more. I don't see it in restaurants the way you see other desserts.
The most American food for me is the cheeseburger (with or without the fries and cole slaw).