The wife unit and I went to Newport RI last summer, what an awesome summer vacation spot. If you've never been you're going to love it. I was with a buddy and his wife and his wife had gone to college there so we had pretty good tour guides. Lots of great seafood. You have to take a tour of the mansions and walk / run the cliff trail. I'll list a few of my favorites:
Brick Alley Pub - It's a good pub, get the clams. Outstanding.
The Mooring - Seafood, a little pricy but you get great seafood for the money and its in a nice spot.
Castle Hill - This place has the best view in town, it's out of the way on a point with a beautiful view of the sea, I'd suggest going for lunch and sit out on the lawn and watch the sailboats go in and out. You will probably end up getting laid.
Midtown Oyster Bar - Well, it's an oyster bar. If you like oysters you'll be in the right spot.
Newport RI Mansions - Go see as many as you can, obviously don't miss the Breakers.
Take a jog or walk on the cliffs - not that long of a trail and you can even negotiate it if you are a fat turd.
As for Boston there are too many good places to even start. Id say go to the North End and have a great seafood or Italian meal. It can be a pain to get in sometimes so if you're not there on a weekend it would be better.
Neptune Oyster Bar - They don't take reservations so good luck.
You have to get yourself a good lobster roll while you're there, I have investigated this subject deeply. I could make several suggestions, however I will only make one, primarily because of it's proximity to Harpoon Brewery.
Yankee Lobster Company - Don't mess around, get the lobster roll and maybe a chowder.
Then walk your completely satisfied ass down to the
Harpoon Brewery and have a few IPAs.
Go to Chinatown and have Dim Sum for brunch. First you eat dim sum, dim sum more. Trust me, it's all that and dim sum.