Uber is extremely expensive(I am talking $50-$80 one way to get to the airport) and not reliable on the Island. Many drivers don't want to go all the way out to Aulani to pick up or drop off a fare when there are so many in the Waikiki area that they can get to faster and make more money. If you plan on doing anything, you need a car. Prices fluctuate for car rentals on a daily basis and the best prices are usually 3-6 weeks out. Of course, this depends on your plans. If you are planning a Hawaiian vacation, where you go out and explore, then you definitely need a car. If you are not planning on leaving your hotel, then you can get away with not having a car. The closest town is Kapolei and there are several companies that do deliver from there. Instacart, Shipt, etc. Just Google it and they will pop up.