Thanks for playing!
There are 4 equippable items in the game, but 2 of them are optional. One is hidden in a secret location in the dungeon, and the other (the Laser Pointer) is an item I was going to use for a second dungeon, but didn't have time. You can buy the Laser Pointer in Luna City and use it to distract enemies (Goblobs will jump toward it, Poisonblooms will swipe at it instead of the player, etc.). So if someone is having trouble with the boss, it can be worth the time to grind some Gemcoins to get it. I don't want to spoil what the hidden item does, but it's something longtime Zelda fans are sure to appreciate :)