Couple of things to do:
1. eat lobsters( this you must know already...)
2.Go to Thuder Hole (some steps required).
3. Go to the mountain to see sun rise.
4. Gather fresh clams or mussels at beach to eat.
5. Go to the middle of the south side of the island where there is a bay to watch tide rises and recedes
6. Visit light house.
7. See whale and sea birds.