Lucky you, I would love to go to Hawaii -thrifts or no thrifts. I would have liked to have gone when they were still filming Lost there, that would have been a dream true to see one of their sets!
A new Goodwill opened recently in Amherst, MA which is a short drive but I haven't even bothered to check it out as I am totally unimpressed with Goodwill in general. This one is right down the street form UMass too, which you would think would make it cheaper, but college town thrifts tend to be more expensive.
One thing you might find in Hawaii is beautiful beach glass. I have seen people from Hawaii selling it on Ebay and it goes for good $. I am sure you can find lots of other neat shells, etc. on the beaches too. I guess if you don't find any treasures thifting in Hawaii you might find some in nature!
We went on a movie tour and they took us to a few of the places Lost filmed. The one that I remember the most was a large hill that was used for Hurley's golf course. Lost & a lot of other movies and television shows do a lot of their filming at Kualoa Ranch. Presently they're filming Hawaii Five-O there; unfortunately, they weren't filming there that particular day.
Since we had a lot of activities already planned we only went to the beach twice, but surprisingly I rarely saw any seashells. Someone said that the seashells may get stuck in some of the reefs.