Honestly, I don’t think it exists. People (from the US and not) usually think of fast food and other junk because there’s an overabundance of it. You can easily find things like McDonalds, Coca-Cola, and HFCS filled snacks and beverages in all 50 states, plus it’s cheap making it accessible to everyone.

Outside of that, I think common Thanksgiving foods (turkey, ham, potatoes, pie, Mac n cheese), hot dogs and burgers (since it’s common to grill those 2 things in the summer) are the closest we can get to unifying the country under food.

When people ask me my favorite American foods, more often than not, it’s something they never knew was considered American. I was surprised when I saw a Cajun/Creole restaurant in Taiwan because I’ve never met anyone who knew what gumbo and jambalaya were unless they’ve been to Louisiana or nearby states.

Like much of the “new world” US cuisine is a mixture of all ethnic groups who have lived on that land for a long period of time. Processed/fast food culture just became more dominant within the last few decades. As people became busier, it became the perfect opportunity to advertise quick, easy long lasting food options over making things from scratch like previous generations.