To Eat:

Kokohead Cafe: go there for breakfast
Boots and Kimos: go there for breakfast
Ono Seafood: Best Poke I had there
Leonard's Bakery: They have this tasty treat called a Malasado. Yummy!
Giovanni's Shrimp truck: best shrimp, also up by North Shore

Hikes:

Pill Box: easy, great views
Makapuu Tide pools: You have to do a kinda steep hike down, but doable and worth it
Diamond Head: easy, touristy, but great views

Beaches:
Lanikai: best sand, white sand
China Walls: best sunset. Not really a beach, but a rock wall. Best sunset tho
North Shore: goes without saying

**Don't let people get you down about Oahu. It's a great island. Best food of all the islands, IMO. Tons of great beaches and great hikes.