For the past ten years, we have rented a place in Damariscotta, Maine for two weeks every summer. Here is a list of things that I would recommend, going north from Portland to Bar Harbor on Route 1:
1. Go to the gigantic L.L. Bean store in Freeport, as well as some of the other clothing outlets on the main street. We don't go anymore, but it is a shopping experience not to be missed by a 14 year old girl.
2. Go to Orr's and Bailey's Islands in Casco Bay (yes, you can drive there). Have lunch at Cook's Lobster House on Baileys Island. If you don't sit outside, get a table with a view of the famous Bailey's Island Bridge, the only cribstone bridge in the world (over which you will have driven to get there).
3. Stop in Wiscasset, Maine and shop in all the antique and used book stores and art galleries. You might be tempted by a lobster roll from Red's, but Sarah's across the road is a better place to eat.
4. Go to the Coastal Maine Botanical Gardens in Boothbay. Coastal Maine Botanical Gardens: Discover Spectacular Gardens and Waterfront Landscapes on 250 Acres in Boothbay, Maine - Coastal Maine Botanical Gardens
You might visit Boothbay Harbor while you are there (we think it is kitschy and prefer Camden instead)
5. Damariscotta has a nice downtown shopping area. The Coastal Maine Book Store is a great independent book store. A good meal can be had at the Damariscotta River Grill or, if you've not yet had your fill of them, go to Larson's Lunch Box for a lobster roll. We think they're the best in Maine. Drive down the peninsula to Pemaquid Light, which is one of the most picturesque lighthouses on the Maine coast.
6. Stop at Moody's Diner in Waldoboro for the blueberry pie. http://www.moodysdiner.com/
7. Stop in Rockland and take a windjammer day cruise on Penobscot Bay. Look online as there are a variety of choices. While you're there, visit the Farnsworth Art Museum, particularly if you are fans of Andrew Wyeth. Farnsworth Art Museum | Celebrating Maine's Role in American Art
You might also enjoy a drive/hike out to Owl's Head light, which has got to be the best base housing in the Coast Guard. Owl's Head Lighthouse, Owl's Head, Maine
8. Go to Camden, which I think is one of the most beautiful towns in existence. Hike up Mount Megunticook, in Camden Hills State Park for a spectacular view of town (you can start on the trail right from downtown) or drive out five minutes and climb the trail to the Maiden Cliff on the other side of the mountain. Maine Bureau of Parks & Lands - Search for Parks and Properties
When you get back down, have lunch at the Waterfront Restaurant. http://www.waterfrontcamden.com/
There is a lot more to do in Maine, but for the part between Portland and Bar Harbor, I think these are the best.
Have a great trip!