Fruit stands are great for fruit. Not so great for other produce. Don't recall ever seeing a potato, carrot, or salad veggie at a fruit stand, which might be what the poster is looking for. If you go when Hawaiian sweet corn is in season, buy it from whomever you see set up on the side of the road. Some things NOT to try: noni, breadfruit, durian.
On one of my recent visits to HI, there was a parsnip shortage back home. When stores got it back in stock, it was extremely expensive. Even Safeway was cheaper. Personally, I like the convenience of Safeway a lot. Would rather pick up staples there, and consider fruit stands as bonuses.