For Kelly: Anything cropped, neon, or off-the-shoulder will do. You could also spring for a T-shirt with The Max's logo or a Bayside High sweatshirt. Don't forget to spray those bangs up!
For Zack: A blond wig is a must, along with a collared shirt (don't forget you're preppy!), baggy jeans, and old-school high-tops. A giant fake cell phone will really complete the look.