Gaffes

Johnny's plummet down the slope lands him falling into the ski-store entrance and his skis are left in the doorway, but they're not present in the shot of the crowd looking in the doorway.

When the girl is being pulled, the first shot shows that she's crawling but the faraway shot shows her being dragged.

When Johnny's mom talks with him at the bottom of the stairs she holds a box; the position of the newspaper sticking out of the box changes throughout.

When Randy meets Johnny Tsunami and is talking about hooking him up with gear, the white mask around his neck keeps moving from left to right between shots.

When Sam and Emily are hanging off the slope, Sam unclips Emily's board from her feet and it drops to the bottom of the cliff. But when Johnny rushes over and looks down at them over the edge, Emily's board is visibly still clipped to her boots.

When Sam is teaching Johnny to snowboard, he is riding goofy (right foot forward). In later scenes where Johnny is performing more difficult jumps and turns, he is riding regular (left foot forward). This reveals the use of a stunt double.

Whenever Johnny and his friends surf, the guys who are surfing look taller and older: it's too obvious that they're stunt doubles.

When Johnny topples over into the display in the ski store, Emily yells "Johnny, no!" yet her mouth remains closed.

Before Johnny and Johnny Tsunami have their race, Tsunami's mouth doesn't move as he wishes Johnny good luck.

Kauai is the farthest west of the principal Hawaiian Islands, so "moving east to Kauai" as Johnny asks his dad, is not geographically possible.