It's very hard to say, particularly since the United States has many regional and ethnic cuisines. I would mention a few: a) Corn-on-the-cob, in summer. b) Peanut-butter-and-jelly sandwiches. c) Pizza. I'm not kidding about (c). You get a business meeting in a strange city and someone wants to go out for lunch and the group is trying to decide to go... and "how about a pizza place" wins every time. Or, you are at work and your group has completed some project and the boss "let's celebrate," the thing they are most likely to do, for a short, casual celebration, is to call out and have some pizzas brought in.

Vegemite on toast. (Australia) It puts a rose in every cheek!

Tacos =D

On each festival and a big Chinese new year meal for a week or so.

Poutine (Canada)