My wife and I make the trip up to Portland from CT a few times a year.
Go to 1 Industrial Way and visit Bissell Bros, walk 20' to Foundation and grab as much Ephiphany as you can since they have it on today. Then walk around to the back of the building to Austin St Brewing and grab some great brett IPAs. Then you can either leave your car there or drive it 20 secs to Allagash.
If you somehow make it out of there and want to go anywhere else, you can try going downtown. On the way down, you can hit up Great Lost Bear and Maine Homebrew Supply, which is literally next door. Novare Res is by far the best beer bar in Portland. If "Jesse5grain" is there, ask her for suggestions on sours. Another great beer bar that's often overlooked is King's Head down on the water. Food wise down there, I liked Central Provisions, J's Oyster Bar for seafood, or Po Boys and Pickles for bangin sandwiches on the cheap. Thirsty Pig is good, but I expected more. On the outskirts of downtown, hit up Rising Tide. Walking distance from there is Bunker, but I wasn't that impressed with their beer.
You could then go north up to Freeport and hit up Maine Brewing Co, but as someone else said, the brewery visit is kind of a let down. Across from there is Buck's Naked BBQ - been there once and was happy. Nearby is LL Bean and other stores if you are the tourist/shopping type.
If you go south of Portland, check out Barreled Souls-I was very impressed with all of their beers. Also nearby for food is great pizza at When Pigs Fly.
One other place I've been meaning to go is Ebenezer's Pub, but that's more than an hour+ from Portland.
Have a great trip.