In the second "nude swim" scene, Jennifer is shown running towards the water. She strips off her bikini top, then bikini bottom. A few minutes later when she comes out of the water, there is a glimpse of her still wearing her bikini bottom.
At the very beginning while the credits are still rolling, Jennifer washes up on the island but is still laying in the water face-down. You can see her white bikini bottom at this time. When the scene cuts to her getting up on her hands and knees, her green skirt is covering her bikini - even though the last wave had just pushed her skirt even higher toward her waist.
(at around 25 mins) Kelly Brook's character is persuaded to go skinny dipping for the first time. She clearly removes both her bikini top and bottoms. When she exits the water, her bikini bottoms have teleported from the beach back onto her body.
It seems to take a very long time for both men to grow a beard after being stranded on the island for days on end.
At about 45 minutes, Manuel asks Jennifer, "You want some more juice?" The camera angle is from the front and Jennifer's green wrap is covering her bikini top. The camera cuts to a side shot of Jennifer drinking from a coconut and her wrap is now around her waist exposing her bikini top.
In the fishing scene just moments before they notice the fire that sinks the boat which sets up the movie's primary plot element, there is a glimpse of shore shown behind the boat, perhaps 500 feet off. (This is at about 12:18 into the movie.) The movie's over at this point if they're that close to shore: everyone boats to shore and the owners file an insurance claim. Roll credits. The movie only makes sense if this event happens out of sight of land.
Shipwrecked on a deserted island and struggling to survival, Jennifer somehow still keeps her legs, armpits and bikini line clean shaven.
Billy Zane smokes cigars and cigarettes, even though he swam to the island from quite a distance in the ocean. He also has numerous "wardrobe" changes; where these extra shorts, shirts and hats came from is a mystery. The woman gains a hoodie out of nowhere. And items appear such as milk crates, fishing nets, etc. The number of goofs is embarrassingly high.
At one point in the film, Jennifer says that she is not a good swimmer. However, later, after their boat sinks, she and Manuel have to swim the long distance back to the island, and she copes well, even beating Manuel to the beach.