Many of the campers at Camp Half-Blood have their own Magic item. Clarisse has an electric spear. Annabeth has a baseball cap that turns her invisible. What Magic item would make sense for Percy, as the son of the Sea God? Design your own Magic item.
Well he should have a Magic spear of water. He would call it The Master Spear. Let me explain, he would have a spear of water that he can mold into anything, and he can change its shape with his mind. He can change it into an ice spear then throw it at someone or something. Also he can make it as thin or as thick as he pleases. It can fold into a ball. He can make it as big or small as he wants. He also can change it into a snowboard, shield. The bigger it gets the thinner it is. It's pretty cool.