Here are a few ideas:
Nico's Pier 38 Restaurant in the downtown Honolulu area is one of the best seafood restaurants in town. Not fancy, but fish is same-day catch, fresh off the boat. It doesn't ever get better than this. Go during Happy Hour for best pricing (dinner entrees are at Happy Hour pricing.).
https://nicospier38.com
If Hawaiian Culture and history interest you, the Bishop Museum is a must-see. It showcases the entire South Pacific region, with artifacts, dioramas, and great information. Lots of Hawaiian historic items. Plan to spend at least half a day there.
https://www.bishopmuseum.org
And then follow it up with a trip to Iolani Palace, for the rest of the story.
https://www.iolanipalace.org
If you'll have a car, driving over to the Windward Side of the island, stop at the Pali Lookout for an amazing view of that side of the island.
https://www.gohawaii.com/islands/oahu/regions/windward-coast/nuuanu-pali-lookout
Then as you're driving toward the North Shore, stop in Sunset Beach at Ted's Bakery for a piece of Chocolate Haupia Pie. It's legendary.
https://www.tedsbakery.com
In Haleiwa, stop at the Coffee Gallery for some amazing Hawaiian-Grown espresso coffee.
https://www.yelp.com/biz/coffee-gallery-haleiwa
In Waikiki, Duke's is a great beachfront bar and restaurant. Crowded, and getting a table can be a challenge, but the food and drinks are worthwhile.
https://www.dukeswaikiki.com
The Waikiki Aquarium has a fantastic amount of displays that showcase fish from everywhere, with an emphasis on Hawaiian species. There's a tank in front with baby Humuhumunukunukuapua'a that are very friendly.
https://www.waikikiaquarium.org
Friday night the Hilton sets off fireworks just after dark. Make your way to the paved beachwalk in front of the Hale Koa hotel, just next to the Hilton complex, and get a table in the barefoot beach bar out front. Have some food and a drink or two, and watch the fireworks. The Hale Koa is a military hotel, but that beach bar is open to the public. Any night is good, but if you want to see the fireworks, Fridays are the night to go.
https://www.halekoa.com/dining-drinks/barefoot-bar
Dave