J&D Plum Island Provisions. Emerging from the iconic Dick's Variety, via the previous iteration of PIP, this is once again the neswest kid on the block under a recent change in ownership. Serving an extensive selection of seafood, pizzas, and sandwiches, along with general supplies and sundries, including newspapers (although the Sunday New York Times often runs out early).
Click here to visit their website, including a very ambitious menu, and here for a Google satellite map/image of downtown (!) Plum Island with the old/new location highlighted. Currently closed Tuesdays. Great pizzas, and they deliver (with a nominal charge).