If you make it out of Boston, go to Rhode Island. You can try a clam bake there. Lobsters are available all over (they actually are pretty much anywhere in New England, not just in/from Maine). The chowda (the ah's ah dropped in MA, RI,and ME) is not thick and gloppy, in fact it isn't made with milk (just clam broth). You will probably recognize the Clam Cakes as fritters (just the taste will be different), and the Johnny Cake is from here too. If someone offers you a coffee cabinet, don't mistake it for the place in the kitchen where the food is stored (a cabinet is a milkshake with ice cream - called a frappe in MA, and coffee everything is a specialty of RI). The Italian food is better in Providence than it is in Boston (I'll get flamed over that one).
And when a Bay Stater asks you if you'd like a "co-hog", tell him you just had a stuffie made with quahaug (quaw-hawg).