Burgers, pizza, potatoes of any kind, Mac and cheese, steak, cheap junk foods.
I know you said one, but I can pick any one of these.

Do you have a buffet dining hall?

Oh yes. Maybe you can't already, but in a few pounds you'll find you can't really go standing up, your dick coated in fat and hard to reach to control. Your ass and back fat will cover more and more of the back of the toilet, be sure to pull your shirt up higher. You'll have to put your fupa kind of on the seat, dick below with fat above, too bulky to fit.
As you grow wider, you'll either have to squeeze around the stall door and brush against the walls, or start using handicap stalls exclusively, if you have them.
I think you'll also regularly find standard toilets too low, forcing your legs into your gut and making it harder to stand back up.
Oh, and one other thing. Get heavy enough, and you'll break the seat, like I did.

If you ease into eat, like eating until you're full, then just a bit more, it's easy. I, and I feel most gainers here, stuffed ourselves to a bit of pain occasionally instead.

56.6 as of today.

Macaroni and cheese? Maybe not the most calorific, but definitely fattening.

I noticed my stomach hanging lower still this week. Now when I lift each leg to walk, I find my thigh pushing my lower stomach up and sending a ripple up my gut. Even my moobs jiggle a bit. I don't know what I've been eating to do it, but I'm feeling a lot softer, as well as heavier.

The RKO?
Outta nowhere?

Yeah, to me it's a weird way to encourage more gaining. Like everyone truly fat weighs over 600.

I guess there is an element of guilt to the whole experience, if you allow yourself to feel it. Guilt for greedy eating, taking up more space and resources, and guilt for breaking things with newfound weight especially, seats cracking and beds bending.
Your enjoyment of eating and/or being fatter just needs to outweigh (heh) your reservations.