Glad you're traveling again, Mac. Boston is my home town, and October is THE BEST MONTH.
Where are you staying in the city? I'd walk the Freedom Trail if you're feeling up to it. Go down to the waterfront. Boston Common and Charles Street are fun places to hang out.
Newbury Street is fancy shopping and also has a few fun bistros and coffee shops.
The Science Museum is excellent.
Plenty of seafood to be had. New England clam chowder is great if you have sweater-weather.
Go whale-watching right out of Boston Harbor or walk along the Charles River for a great view. You can walk to the Science Museum if you are staying nearby.
My favorite excursions are to Walden Pond (of Thoreau fame) and to stop at apple cider/apple vendors on RT. 2.
Salem Village is another great escape, if you like history as much as I do. And Plimoth Plantation too. http://www.plimoth.org/
The North Shore of Boston has white sand beaches. And there's always Cape Cod, 90 minutes away. I can give you lots more ideas if you need them.
I always drive up RT 2 from Boston to I 91 and RT 30 to Vermont to see my family. Sometimes I catch great leaves along the way, but the last few years the Vermont leaves have peaked in September. Still a gorgeous drive.