3 days, for NYC? Just stay home.
Seriously, what are your & their interests? I spent 9 days there about 10 years ago, & could have spent 9 months without really scratching the surface.
We did a lot of museums, mostly. One almost every day. MoMA, Guggenheim, Intrepid, Natural History, etc.
Went to a Mets game.
Just walked around with our heads in the air taking in all the amazing architecture, broadcasting our tourist status (Never. Ever. Look at anything but the sidewalk, if you don't want to be identified as a tourist.)
If they're into music...Nah; don't even try.
Subways & buses will get you within a couple of blocks of anything you might want to see.
I'm sure that locals can give you better, current info on food, but you shouldn't go hungry.
Charlie