Is it “Macaroni, cheese, and steak” or “Macaroni and cheese and steak”?

It depends.

'Macaroni and cheese' can be a set phrase for a set dish or it can be two separate things.

If you are having two things, macaroni and cheese (a single dish) and another dish (steak) then you'd say 'Macaroni and cheese, and steak'.

But if you are having three separate things, macaroni (the pasta) and also a steak (the meat) and some cheese (maybe as a separate course, maybe sprinkled on top of everything, maybe as a melted condiment to pour on you steak) then you'd have 'macaroni, cheese, and steak'

In British English the name of the dish is macaroni cheese, so you'd have "steak and macaroni cheese" (though the combination isn't common here). As one accompanies the other, with is useful: "macaroni and cheese with steak" or better still "steak with macaroni and cheese". That could still be misconstrued as steak plus plain macaroni plus cheese, but that would be unusual.