Diamond Head is and iconic landmark on Oahu and an extinct volcano. The hike gives you a great view of Waikiki. It's an easier hike, may charge a modest $5, but it is quick and close by, and finishes with a nice view. If you want to cool off afterwards, Diamond Head beach park is a nice relaxing beach away from the hustle and bustle of Waikiki.
Hanauma Bay is a protected cove with a coral reef to snorkel and see an abundance of fish. It's run by the state, so there is an entrance fee, but because of the vibrant coral reef, it's one of the best spots to snorkel on the south side.
This is a tough hike that is straight up 1,000 railroad ties to a great view of Oahu. It's an ass kicker of a hike and Hawaii gets hot, so if you are going to do it, do it early. Sunrise is ideal! DO NOT ATTEMPT IF YOU HAVE ANY HEALTH ISSUES.
Rainbow drive-in is a classic spot for plate lunch. It's not traditional Hawaiian food, but it's local food that has been around for ages. If you're working on your beach bod, this food is not good for you, but it's good for your soul. I highly recommend working off the hangover the morning after the wedding with a nice loco moco from Rainbows.
Leonards bakery sells more than just malasadas, but that's what they are famous for and I wouldn't be doing this recommendations list justice if I left this staple off. Malasadas are a Portuguese fried pastry, similar to a sugar donut, and legend has it Leonard and his wife brought them to Hawaii and made them a mainstay.
If you don’t have time or the means to get both baked goods at Leonard’s bakery and plate lunch at rainbow drive-in, Liliha Bakery is your one-stop shop for both. There are a few on Oahu, including at the Ala Moana mall. The most conveniently located one for this event is right across the street from the Royal Hawaiian Hotel at International Market Place. However, if you do indulge in both their hearty Loco Moco with Fried Rice and their delicious Coco Puffs (cream puffs), be prepared for a food coma immediately to follow. Luckily, a nap on the beach is just steps away.
If you have the means to get to the North Shore, Sharks Cove is a nice public snorkeling spot free of charge. The name may sound scary, but you're more likely to have to worry about sharp rocks cutting your feet than sharp shark teeth. The tide pools are a great place to check out schools of fish, however it is located on North Shore so be weary of the swells. October is close to big wave season on North Shore, and although Sharks Cove has some protection, be aware of the waves if you go.
The Polynesian Culture center is a great tourist spot to learn about the Hawaiian and other Pacific Islands. It is on the north shore, so would require a car or shuttle to get there from Waikiki, but it's a great way to learn about the culture, the people, and best of all, the food if you stay for their Luau.
If you are willing to drive for a bite to eat, Kahuku sugar mill has options for everybody. Numerous stands and food trucks have been featured in food shows from Ry's Poke Shack or Da Bald Guy on Netflix's "Street Food USA," or Mike's Huli Chicken on Triple D, and of course there are countless shrimp trucks in the area as well. The drive may seem far for a bite to eat, but down the road on North Shore there are the world famous surf break like Pipeline, as well as Haleiwa has tons of shops and art galleries, as well as Matsumoto Shave Ice, and Kawela Bay beach park is a nice secluded beach that has been the set for movies and shows like "Pirates of the Carribbean," "Hunger Games," "Lost" and "Hawaii 5-0" and more.
In case you forgot something at home, or don't want to worry about traveling with party clothes, the Ala Moana Center is the spot for you. It's a typical mall with plenty of stores for all your various needs.
Pearl Harbor National Memorial museums & grounds are free. Program reservations are recommended.
Boat tour company for snorkeling or trips on the west side of Oahu. A great time if you enjoy being on or in the ocean.