There is a sign on the door of Pleasure Pizza in the scene before Kim and Jay first kiss with a phone number that has 831 as the area code. The area code for Santa Cruz and Capitola was still 408 in 1994. The change to 831 happened in '98.
When Jay is out in the water searching for Frosty, he throws the bottle cap into the water and puts the bottle without the cap back on the board. When he peddles further the bottle cap is back on the bottle.
In the beginning when Kim throws the ball the first time for her dog to chase we see she is standing in Ice Plant, something that grows everywhere near beaches in Southern California, and where it grows nothing else makes it through. But when the camera shifts to show the dog retrieve the ball it's now showing just regular weeds like dandelions with no Ice Plant anywhere even though in the initial shot we saw that she was surrounded by it.
In the scene(s) where Jay sneaks onto the top of Frosty's van and gets his first look at Mavericks, when they are driving home, there is a red and green surfboard on the top of Frosty's van. During the trip home the surfboards change location on the top of the van; green on the left, red on the right to green on the right, red on the left, etc.
In an early morning scene, a surfer is looking out a bluff to the ocean waves down below. The rising sunshine comes in from the left hand side of the frame. Even on the most south facing beach in Calif., the sun raising behind the scene.