Iced tea and popovers in the afternoon at the Jordan Pond House in Acadia National Park.
Whale watch boat trip.
There's some local boat trips to the nearby islands that are worth checking out.
There's another boat trip (I think it was out of one of the other harbors, not Bar Harbor) that had a Park Ranger on it, a naturalist trip, that was good. I remember seeing this incrediably tall Osprey nest.
Of course there's always lobster, if you like lobster (not my bag but my wife and son loved it).