What you need depends partly on your age. What you will definitely need are a pwc, whistle (or horn), fire extinguisher and uscg approved personal flotation device (life vest). If you are under a certain age (I can't remember if it's 16 or 18) you will need a boater safety certificate from a required safety training class.
Other optional items are shoes (Slippery makes a popular pair, don't last very long but are comfortable; Asics or other brands of wrestling shoes also work well and last a bit longer), wetsuit/ride pants/shorts (Jet Pilot, Slippery, Quakeysense, and many others have several styles and colors to choose a wetsuit from; Slippery and Fly Racing both have a freeride pant with zip off legs; then there are board shorts that work well to keep your hind-side covered after a high speed spill), rash guard, gloves, helmet, knee brace. Oh yeah, almost forgot, Parrdaddy sports the Speedo panties as well. I'm sure others will have suggestions on gear. Take everybodies info and decide what is best for you.