Okay, after giving it some thought, here is a few things:
Whale Watch
Boston Harbor Cruises
New England Aquarium
Boston Duck Tours
Trolley Tour
top of the Prudential Center
A bit on the pricy side, but for restaurants and if you like seafood, Legal Seafood on the harbor is world famous.
You can also walk the Freedom Trail for free, just follow the red bricks =)
When you buy a trolley ticket, you get a day pass and can freely get on and off trolleys. They stop at major attractions and you can get off and see if any of those places interest you.