Kosher near the American Museum of Natural History?
Anything still there worth going - casual for sunday lunch?
Alibaba is probably the best casual option nearby. The new place on Amsterdam and 77th or so--Hummus Place, I think it's called--should fit the bill once it's open, if it hasn't already.
From what I hear Makor Cafe has a great Sunday bruch - take the subway in the basement of the museum one stop to 72nd street - exit at front of train - then walk 2-3 blocks down Central Park West to 67th street, make a right and makor is 2/3 of way down the block on the north side of 67 (www.makor.org) - prices are very very reasonable, ambience is great and food is even better