For grab and go, there are a number of very good places worth a visit.
RELISH at 93 Commercial St. is a west-end favorite for its dependable sandwiches, pre-made salads and if you like your baked goods quite sweet there is a great selection, albeit pricey ones. Here the food is a bit more upmarket.
POP & DUTCH at 147 Commercial St. is a shabby chic establishment with excellent sandwiches, a large selection of very good prepared salads and sides, and a few window seats for those staying. The choices don't vary much but they are reliable.
ANGEL FOODS at 467 Commercial St. is an east-end choice that is a full-on grocery store (albeit a small one) with prepared dishes for take-away that can be quite terrific. Advantages include a parking lot and its few outdoor ramshackle seats near the water's edge providing a splendid view.
MAC’S SEAFOOD MARKET at 85 Shank Painter Rd. may be thought of as the fish market adjunct to Mac’s restaurant but it offers quite a bit more. It’s a reliable place to buy fresh raw seafood for home cooking. It also has many very good pre-cooked takeaways including fish cakes, lobster salad, daily chowder and more. You can work up an appetite by peddling your rear end up Shank Painter Rd.
I will mention FAR LAND PROVISIONS at 150 Bradford St. because it has been a town favorite for some time. I have found it to be a mixed bag of good coffee, quirky but tasty sandwiches and oddball treats. You might want to favor the main shop at this Bradford address and skip their Herring Cove beach outpost which is best only for a cool drink or those desperately hungry.