I need to leave my car in a cape cod parking lot that is close to the ferryboat, for the whole weekend. which would be the most advisable?

Palmer Parking Lot in Falmouth is where I park. Its 15 dollars a day in the summer and has a free shuttle to the ferry. No restrictions on length of stay from what I have seen

Yes, you can leave your car in the Steamship Authority Parking Lot for multiple days. More details on daily rates and specifics can be found through the following link: https://www.steamshipauthority.com/traveling_today/parking