Magic items

Magic Items are used by characters for a lot of stuff, they use them in Capture the Flag, fighting and other stuff.

Riptide
Percy Jackson was given Riptide by Chiron in The Lightning Thief to fight against his "teacher" Mrs. Dodds (AKA a Furie). It is made out of celestrial bronze witch will not harm mortals but will "pass through them like an illusion". It is magic in that it can not be lost, if you through it away it will apear in your pocket a few moments later.

Hermes' Gifts
As Percy is leaving on the quest in The Sea Of Monsters he sees Hermes who gives him some gifts.

Vitamins
Hermes gives Percy some vitamins that counteract all magic for a time. Percy uses those to excape from being a guinea pig after being turned into one by Circe.

Thermos of winds
Hermes gives Percy a thermos that contains the four winds of the North, South, East, and West. Percy lets one wind go to gain speed to catch up with Clariese, and the rest to fall away from the center of a whirlpool.