I don't know what your tastes are or anything, but
axeman9182 is on point with the Ani Ramen suggestion. That would be my top pick. However, I haven't been there in like a year because it is ALWAYS crowded af, so you should have some backups just in case. But if you do make it in, I tend to order and can highly recommend the mazeman.
There's a taco place right down the street from Ani called Villalobos that is pretty good, kinda pricey. There's a better version of that same restaurant (in that Villalobos shamelessly ripped off this place) in Bloomfield called El Matador that I would highly recommend.
I feel like I'm always recommending Mesob, which is an Ethiopian place that I absolutely love, but may not be for you. But if you like eating small piles of meat and veggies with your hands, some very spicy, some not at all, using hunks of spongy bread to pick it up, give it a shot.
I'm not a fan of The Office, but you can usually get like a Founders All Day and some pub food, so if thats what you're in the mood for, by all means go for it.
If you want to spend a little money, have a great meal, a great cocktail, and a decent beer selection, Pig and Prince is outstanding.
Egan's is hot garbage, don't go there.
But I would say the single best place that kind of has everything I want in one location is either Cowan's (which is in Nutley) or The Barrow House (which is in Clifton, so closer). Neither is more than 10 minutes from Montclair, but if you have limited time, or won't have a car with you, then they're not especially accessible.
That's everything off the top of my head. But you can feel free to PM me if you need anything else.