I just finished the game and there are two items that were never used. One is the banana, the other is the fish food. What do they do exactly?

I don't know about the banana, but I remember that I used the fish food on the aquarium in Eddie Chang's apartment. (Though it didn't do much besides giving some points.)

bandana , also found in chang's place

Fish food was answered, don't know about the other...

You can also check the hints in game on where to use them.

In the same room where you get the bandana, there is a display case with different artifacts on the back wall. On the side of the case is a sign and you use the bandana to wipe off the dirt.



There is also a lever below the sign . Anyone know what happens when you pull the lever?

The switch IIRC vaporizes the pieces in Ching's collection, which doesn't do anything except detract from your score.

Use the fishfood on the open aquarium. Tex will eat it instead of giving it to the fishes. Other than that, it has no active function.,