Hawaii is a place that resists an itinerary.
We spent our time hanging out at the pool or on the beach, or trying to find the best poke on the island.
We hired a car for one day while we were there and did a lap around the island, visiting the Dole Plantation (which had good ice-cream but was otherwise fairly dull, and featured a tutorial on how to cut a pineapple (?!)) as well as beaches on the North Shore.
If you plan to travel to Hawaii, I recommend avoiding accommodation in the overpriced hotels in Waikiki and trying your luck with an airbnb or similar, especially if you can find somewhere past the mountains. The beaches are better, there are fewer tourists, and you can see more of the true Hawaii.
The hotels in Waikiki tend to charge a daily "resort fee", hidden in the small print, regardless of whether they are in a resort or not, of around $30-40.
I recommend "Dukes" in Waikiki for their hula pie.
If you have never tried poke before, there is a panoply of places in Hawaii to get it from, ranging from corner shops to supermarkets, and you owe it to yourself to try.
We went to the obligatory luau, choosing one at the aquarium in Waikiki which was quite lovely.
Overall a great trip and much more affordable than you would expect.