mackeral, live, whole, chunk whatever, make sure it's fresh. Sandworms, or bloodworms, are also killer and will catch stripers year round at Popham.
but bring some artificials like big mackeral poppers and spooks, in mackeral patterns, EARLY in the morning; you might get surprised with a major explosion on top, usually the fish tend to be bigger. You won't get that thrill with bait. Try it you'll like it.