one option is to drive to Lowell MA and park your car at the commuter train station, take the commuter train, it drops you at north station, and from there you can catch the T to anywhere it runs. You can also drop your car in Cambridge at the Alewife station, and take the T directly in to town, this might be more direct to 95.
to get to the constitution, you need to get to the Charlestown Navy yard, you can get there by the T using subway, but you can also use the water shuttles, (also part of the T system).
Totally jealous, I'm a new englander and haven't been home in a while, is there room in your suitcase for me??