We have rented a few houses on and off the island via VRBO. They all had water access and were all fantastic.
Bernard Cove
South east of Southwest Harbor
Trenton
We try to time the drive up to get lunch at Flo's in Cape Neddick, ME. Earlier is better because the line can snake out around the parking lot. Read the sign out front regarding how to order. The "special" with their relish and mayo is great. Follow it up with ice cream at Dunne's in York, out on the nubble. Park at Sohier Park to see the lighthouse and brave kayakers.
http://www.floshotdogs.com/
Get your 7 day vehicle pass at the visitor center. You need the pass for park access even at the areas not hidden behind a gate.
https://www.nps.gov/acad/planyourvisit/fees.htm
Take the bus when you can. Parking is tight in the park. Every bus has a 2 or 3 bike rack front and rear. There is a bike specific shuttle (van with a trailer for up to 15 bikes) between Bar Harbor and Eagle lake.
http://www.exploreacadia.com/
Diver Ed - This is a boat ride around the harbor. You will stop somehwere so Ed can dive. You can watch on flat screens in the boat while he looks for interesting sea creatures. He will bring some back onto the boat to give you a chance to touch some sea life from the bottom. Great for kids,
https://www.divered.com/
Whale watching tour - I don't remember which boat we took but they promised a whale sighting or free return passes. We actually got the free tickets and went again 2 years later. Bring warm stuff to wear.
Lots of hiking - Everything is good. Take the braver kids on the Beehive or Precipice Trail. Both of these require climbing via steel rungs and handrails pounded into the rocks.
Dan Falt wood sculpture barn - If his barn is open, the kids can paint some small wood animals for a donation. We have a brace of his fish, painted by the kids, hanging in our kitchen.
Biking the carriage trails - Plan a route and explore. I usually take the whole pack on a short ride. Try a loop around Witch Hole Pond. You can combine biking and hiking as well. I took a little one on a ride from the Bubble Pond lot to behind Conner's Nubble then we hiked up to the Nubble on foot. When I want to take a long ride, I'll leave the car with the pack at the house and take whatever bus rides I need to get to Eagle Lake. Catch the local bus and either pull the cord as you drive by Eagle Lake (or other desired stop) or catch the bike shuttle at Bar Harbor. I imagine that any cyclocross suitable tire will do well enough on the fine gravel trails. My 26 inch hardtail with 2.25 tires was more than sufficient.
Watch the sun set from the top of Cadillac Mountain - You have to drive up an hour or two before sunset as there is limited parking. The rangers will close the road if/when the top is full. Or, pedal your arse up the hill. Bring dinner and a bottle of wine.
Find a good lobster pound. Ours is Thurston's in Bernard.
Schoodic Penninsula - Don't forget that part of the park is across the bay on Schoodic Penninsula. We saw eagles and their nests while touring around.
Jordan Pond House - This is a wonderful place to sit and eat on a nice day. Traffic and parking can be a nightmare so take the bus if you can. Get there early.
Popovers - Eat lots of them! You don't have to go to Jordan Pond House to get your carb fix. The Common Good in Southwest Harbor offers popover breakfast in exchange for a donation. You can usually walk right in to their outdoor eating area. Donations go towards helping feed people in the off season. Please be generous.
http://www.commongoodsoupkitchen.org/