I lived on Oahu for 3 years. Granted it was in the 90s, but have been back a few times. Some ageless advice for Oahu.
Food:
Malasada's at Leonard's. Portuguese donuts. They are widely available but Leonard's is classic. Oh, the rest of their baked good don't suck either.
https://www.leonardshawaii.com/home/
While you are in the neighborhood, plate lunch at the Rainbow Drive In (no, you don't have to eat in your car).
https://rainbowdrivein.com Do not substitute out the two scoops rice and scoop macaroni salad, unless it is to replace one of the scoops of rice with an extra scoop of macaroni salad. If your plate doesn't include gravy and they ask if you want it, say yes. There are now three locations, but the original and best is off of Kapahulu. Leonard's is just up the road.
Shave Ice (First under Benny's don't be a Haole list, DO NOT, for all that is holy, call it shaved ice). Don't get it in Waikiki. Trucks on the north shore are fine. My favorite is a bit touristy, but I like Island Snow on the north side of the island in Kailua.
I have a fond place in my heart for Auntie Pasto's off of King Street for basic good Italian food.
If you see a food truck in Thomas Square, get a plate lunch there.
Other general food suggestions:
Huli Huli Chicken, especially if is it roadside or a fund raiser. But any local place that serves it, it is wonderful.
Kalua pig - heavenly.
Waikiki
Okay, if you are going to go and likely stay in Waikiki. Amazingly enough, there are some good things to do there.
Breakfast at the Veranda at the Westin Surfrider. Yes, it is pricey, but good food and the view and setting is spectacular. Option B is to at least have a drink there, sitting under the massive Bayon tree.
For Jimmy Buffett fans, the original Duke's at the Outrigger was one of his favorite places (mine too!). Good seafood, but even just a drink and enjoy the view.
Catamaran ride. Touristy, yes, but the views are spectacular. I prefer the red and yellow boat over the blue and white or more recent newcomers, but that might be more for nostalgia, as I knew the captain and crew in the day. Ride up front in the netting for a bit just to get the experience. (I think it is still all you can drink included in the price) Back in the day, it actually used to be by the drink and the cheapest place to drink on Waikiki.
A drink, preferably around sunset at the Mai Tai bar at the historic Royal Hawaiian Hotel. Just for the history. Oh, and the setting isn't bad.
For fine dining (make reservations) House Without a Key. Everything is locally sourced. Go with whatever the chef is recommending that day.
Things to do:
As Benny noted visitors will send a ton of recommendations. None are probably bad.
A couple off the wall ideas:
Bishop Museum for all things Polynesian.
I'olani Palace - Be respectful. It was the last home of the queen before the US overthrew her.
Hiking - there are a ton of hiking trails very close to the city. Many are not crowded unlike the popular ones like Manoa Falls. But be warned, don't leave valuables in your car especially in plain sight.
Punch Bowl Crater National Cemetery. Spectacular. And great views of Honolulu.
The North Shore - Especially in winter can be spectacular....and crowded. Parking can be a challenge. Waimea Bay is amazing. But Shark's Cove just up the road can be cool as well and easier to park. It is wild that the North Shore can have 20 foot waves in the winter and flat calm in the summer.
State fish is humuhumunukunukuapua'a (that's 9 u's Bob).
They don't use east west, north south - Mauka is toward the mountains, makai is toward the water. Ewa (pronouced Eva) is to the west, koko is toward the east.
Don't eat the Spam musubi, especially from the ABC store, no matter how drunk you are.
Not at all a definitive list or even a best of. And like I said, it has been before Covid since I have been, but feel free to ask if you have specific questions.
