No "can't miss", but you should hit up: Honolulu Beerworks, The Village Bottleshop, REAL Gastropub, BeerLabHI, Brew'd. Possibly the new Maui tasting room on da Strip, Tamura's for bottles & Whole Foods Kahala for draft+bottles. Still somewhat better to import your own via checked luggage.
I always bring my own bottles and cans with me to the Big Island. Then I'll stop by Big Island BrewHaus for fresh bottles to go. On Oahu you probably have more choices. I try and stay away from the island Oahu.
You looking for local brews or things to take? Local brews would be BeerLab. Bottle shop would be Village. Where are you staying and do you have a car?
