Larsen's
Basically a retail fish store, Larsen's has a raw take-out counter and will also boil lobsters for you. Dig into a plate of fresh littlenecks or cherrystones; oysters are not a bad alternative. There's also seafood chowder and a variety of smoked fish and dips. Bring your own bottle of wine or beer, buy your dinner here, and then set up on the rocks, the docks, or the beach: there's no finer alfresco rustic dining on the island. Sunset-watching is wildly popular here; call ahead or expect to wait a bit.