A water polo goal, a shot clock, a score board, a water polo ball, and last but not least the player. Water polo swimming apparel are speedos, and a cap saying the number/team color. No goggles are worn.
The basics are a mallet, a helmet (for you), gloves (usually optional) and comfortable clothes. For your horse you do need to snip the mane, polo wraps for their legs, a saddle, light-weight saddle...