My wife and I make it a point to always purchase our nieces and nephew some books when we travel. When we are in Hawaii we can easily find children's books with a Hawaiian theme in most stores that sell souvenirs. We have found some very nice ones with colorful illustrations in the ABC stores and at the Whaler's general Stores.
Our most recent visit to Maui; we found this book for our nephew called Aloha Bear. The story is about a bear looking to escape the chilly North and climbes into Santa's bag for a journey to a warmer place to live; Hawaii. It's a cute book with illustrations that our nephew enjoyed having read to him many times.
If you are staying in a timeshare type resort near Lahaina, and you are flying into OGG
on the way out of the airport when you make a left on the highway 380, stop at Costco and stock up on supplies, the markets on the island are few and far between and really really expensive