The Fat sandwich is the New Brunswick grease-truck category that took the rule every other sub follows, that a long roll should carry a coherent filling, and replaced it with a different rule: put a full fried meal inside the roll, sides included. A cheesesteak or chicken fingers, mozzarella sticks, French fries, and more, stacked into one sub roll, is not a sandwich with a side of fries; the fries are in the sandwich. That inversion is the whole format. The Rutgers truck line runs on a grammar where the bread is asked to contain an entire tray, and the named Fats are just specific orders off that grammar.
The craft is structural triage under impossible odds. Everything in a Fat is fried and hot and was crisp a minute ago, so the build is a race against steam: the components are dropped into the roll straight off the flat-top and the fryer and handed over fast, because every second in a closed roll trades crunch for sog. The roll has to be a long, sturdy sub length with a crust that can take a heavy, greasy, structurally unstable load without splitting down the side, and it is the only thing holding the tray together. The fries are doing double duty as filling and as a starchy floor that soaks the grease that would otherwise reach the bread. The mozzarella sticks are the binding layer, their melted interior gluing the stack as it cools. Lettuce, tomato, and a sauce go in less as nutrition than as the one cold, wet note in a sandwich that is otherwise uniformly fried.
The variations are the named menu. The Fat Cat builds on a cheesesteak base; the Fat Darrell goes meatless-fried with chicken fingers and marinara; the Fat Moon runs cheesesteak with bacon and ketchup; and the truck line keeps generating new ones by swapping the fried center. Each is its own specific stack and deserves its own article rather than being crowded in here.