We booked a 2 1/2 hour tour of Acadia National Park with Oli's Trolley. I recommend that you get tickets on the web in advance. The tickets were about $40 each and well worth it. There are lots of unique shops at the harbor.
We chose to buy tickets for the hop on hop off trolley. It visits the major areas/attractions of the city and picks up/drops off next to the port.
We booked a ship excursion to Peggy's Cove. This place is beautiful and the drive there was very nice.
The Newport Visitors Center is two blocks to the left of where you get off of the tender boat. This city caters to its tourists. You can book tours at the visitor's center. We booked a van tour with others to The Breakers Mansion and scenic ride. They let us off to walk on the Cliff Walk and Sailing Club. We ended at the Breakers where we had city bus tickets to return to the port. This tour cost about $40 each. After our tour, we had The Black Pearl's famous clam chowder.
We booked a ship excursion to the reversing falls and highlights of the town. Tip: If traveling to this port from the South, the time will move forward overnight one hour. Had we known this, we would have booked a later tour.