Do expect to bring your own lunch and cold drinks, but don't bring bananas. They are very bad luck. Shore fishing is a most worthwhile option. Waikiki Fishing opens and closes on a biannual basis, but there's decent action off most breakwaters and many beaches for smaller species. For example, Kaneohe Bay is a particularly nice spot to take bonefish.
Reefs are another option, and where permitted, wharves are a good bet.
Locals rope down cliffs and fish from exposed reefs, but this is a good way to drown. There's limited freshwater fishing in the reservoir across the highway from Schofield Barracks and in stock ponds and canals.