When Gidget gets her lesson on her new surfboard, the fin is broken in half when it rolls over in the water, but is "repaired" when she and Moondoggie reach the beach.
During initiation of Gidget, Hot Shot grabs under her arms and her feet are grabbed by Moondoggie. When they get to the water, her position changes to a chair-like position.
When The Kahuna first goes out to surf the cigar in his mouth is shorter than when he comes back in from surfing.
During the luau scene when Gidget and Moondoggie first arrive, Doug McClure's character is doing a solo dance with a watermelon slice on his head, near the bottom of the steps. Seconds later, when the couple come to the other side of Kahuna's hut, McClure is sitting behind the other guys there playing a conga.
When the girls try to get the boys' attention, Nan picks up the ball and when the shot changes, Gidget has the ball and is tossing it to Nan.
When the Cliff Robertson character and Gidget (Sandra Dee) are drinking Rheingold beer toward the later part of the movie, this beer was primarily an East coast beer and not distributed to California.
The beach location for the film (Leo Carrillo State Beach) has many large volcanic boulders sticking out into the water. Surfers would avoid this area at all costs for its obvious dangers.
When The Four Preps are playing at the luau, they have electric guitars with no amplification cords running from their instruments.
When Gidget comes home from the beach after getting tangled in the kelp, her mother and father view her through the dining room window walking across the lawn. Gidget's mother is setting the table for dinner and places a large salad bowl between the candles on the table. The candles change from blue to cream and then back to blue between the scenes as Gidget comes up the walkway to her house, enters the front door, and walks past the dining room.
When Gidget has completed her first successful surf the gang carry a surf board back to the shack. An audio reel of various ad libs plays during this part. After the Gidget learns of the "orgy" the gang disbands and the very same audio reel of ad libs is heard though it has no relevance this time around.
At @15min mark as Gidget and her dad are walking back from the stairs to the living room you see the shadow of a camera on her dads shoulder.
When "Lover Boy" (Tom Laughlin) is giving Gidget (Sandra Dee) surfing lessons (at 31 minutes in), the shadow of the boom pole and mic can be seen intruding multiple times on the front of the surf board. It's especially visible on the underside of the board when it flips over a few seconds later.
Gidget is told a used surf board costs $25.00. She mentions she only has $4.50 left from her allowance, meaning she only needs $20.50 more. However, when she asks her father for some money, she asks for $21.50 instead of only $20.50.