If you are visiting Kauai for a week or more, I recommend this map. It packs a lot of information front and back. The freebie map from Hawaiian Airlines at the airport is OK, but this is way better. Get it online at https://www.envdhawaii.com/product/kauai-island-atlas-maps/ or look for it in stores around the island. For sure it is available at Kauai Photo Tours in central Kapa'a.
GPS on a phone is great but having a good map with nice visuals and comprehensive information is a good tool. I refer to this map frequently . . . . .