Hilo Hattie's is a fun place to shop for "tourist stuff". The prices aren't bad, and the staff is very helpful. The various craft fairs and roadside booths on the island offer similar stuff, sometimes at better prices, sometimes not.
Forget about getting a bargain on pineapple. The prices on Kauai are no different from those on the mainland. And the shipping costs will eat you alive.
And the Oki Pancake House proclaims itself as "The Home of World-Famous Oki Pancakes." I'm not exactly sure why, as IHOP or any one of a thousand other breakfast houses can do them just as well.