Depending on where you are going on Kauai, wet doesn't begin to cover the climate. The central peak gets around 400 inches of rain a year. Last I checked it was listed as the wettest place on the planet.
Since you're hunting, I'm assuming you are headed for the Na'pali coast. Drier than the interior, but still pretty wet. Either way, finding water to rehydrate dried foods shouldn't be a problem!
Oh, forget packing coffee. Buy local when you get there. Ain't nothing in the states that comes close to real Kona coffee.