When Garner says his line about getting an attitude, Mitch's arms are swinging at his sides. In the next shot, his hands are on his hips.
When Destiny is recovering in Lifeguard HQ, her blanket falls off her shoulders twice.
When Summer swims out to rescue the boater, the strap of her floater changes shoulders between shots.
It is mentioned more than once that Mitch's birthday party takes place on "Sunday night." But when Matt, Summer and Garner go outside to see Matt's new motorcycle, it is clearly daytime.
When Summer is recovering from the accident with the boat, C.J. is holding an ice pack on her head that disappears between shots.
When Matt complains about no one trusting him, he reels off his parents, Stephanie, and Summer. But it wasn't Stephanie who confronted him earlier, it was C.J.