We stayed in a historic cottage quite a bit off the beaten path on the South Shore of Kauai. All the way past the turn off to Waimea Canyon, in the town of Kekaha. Since we mostly spent our time eating in, we scoured the area for the best gluten free friendly grocery stores, farmers markets, and still stopped by a couple of spots recommended by so many others. Overall, to be honest, our time on this part of the island did not live up to the amazing eats we enjoyed on the North Shore. However, with our lodging so isolated, we did manage to come up with one of my favorite new travel meals; green coconut curry with sautéed pineapple and onions.
On the East Shore, near the airport, we did our first grocery store run at Papaya Natural Foods which had a great selection of dried gluten free and allergen friendly goods. On the the other hand, the produce section did leave something to be desired; something I noticed over the entire island. Better to buy your produce at the many farmers markets. The one exception to this rule may be the Living Foods Market in Poi'pu - which had a small but really excellent selection of local produce. Living Foods also has a good selection of healthy and locally made products.
We also made it a point to stop by the island's only gluten free bakery; Sweet Marie's in Lihue. There was a wide selection of mostly muffins and cookies. We tried a few varieties which were all very delicious (and big in size for gluten free) - but very sugary. I can't say they were the best muffins I've ever had, but I suppose if you were in need of a safe gluten free treat I would recommend heading to Sweet Marie's. Otherwise, I'd say I got way more enjoyment out of the amazing local produce than sweets.
As far as restaurants go, the only one we ended up trying on the South Shore was Verde. It's a little hip taqueria located in a strip mall in Kapaa near Papaya Natural Foods. From what I read around the internet, it's definitely hyped as one of the best gluten free friendly options on the island. My experience was somewhat mediocre; the staff needed a lot of coaching to understand my gluten free needs and by the time we got our fish tacos they were completely cold. I didn't get sick, so my food was safe, but again - I'd rather head to a farmers market and gather some fresh eats there.
I keep talking about farmers markets, so let me get to sharing my favorite one on the South Shore. The Kukui'ula Gourmet Farmers Market was quite a bit different than the other markets on the island - purveying more locally produced goods as well as produce. My favorite find were these massive butter avocados and adorable mini pineapples.