Lets get straight to the good stuff, which I mean free.
Free activities– There are a few hikes (smallish) in the Honolulu area. Koko head was probably my favorite and basically its one giant staircase with great views on the top. This should be coupled with snorkeling at Hanuma bay which is opposite (7 dollars to get in-bring snorkeling gear as hire is expensive).
The other one worth visiting is Makuapu’u trial, what was good about this one is you can go off one of the side tracks to get to some awesome tide pools. Other free walks include Diamond head and Manoa Falls.
Free entertainment– On Waikiki beach there is a free Fireworks display on Friday. On Tuesday/Thursday/Saturday between 6:30-7:30 there is a free Luau, basically opposite McDonald’s. Also Pearl Habour is really interesting but make sure to get there by 8am if you want to visit the memorial.
Best Beach– Waimanalo.
Best Food– Gina’s BBQ. Be warned these are FAT men portions.
Top tip- Dont get a taxi or car as the bus network is super cheap and reliable.