Leaping of the Shrew - September 27, 1956 - S5-E3
Revealing mistake: The background while Scott is on the raft with Brooke Shields is blatantly a studio wall. The clouds have streaks on them with dark colors and the seam where the ocean meets the wall can be spotted. The film "The Truman Show" used the same technique.
Deliver Us From Evil - March 19, 1966 - S5-E7
Revealing mistake: When Ilia is spurned by Sam, she sits on the bed and rips her clothes. When she goes to scratch her face, you can see the fake blood on her hand when she goes to smear it on her face.
A Tale of Two Sweeties - February 25, 1958 - S5-E12
Revealing mistake: Sam's reflection in the mirror near the beginning of the episode drops his handkerchief too quickly after wiping his mouth, making things not match up.
Answer: Sam threw items off the raft to lighten the load, so it wouldn't sink, in doing so he made the raft less heavy. Which made easier to float with the currents, if it was heavy the raft would have moved slower and not moved so far.
Except that Al said that immediately after throwing stuff out of the boat four hours passed and it was shown that they didn't really move from where they were. They were still in the same spot. Forgot to ask this too. When Sam and Vanessa are stranded on the island, one of them, can't remember who, did something and when Al appears, he tells them that because of it, time had suddenly skipped several more hours and if the event hadn't been interrupted, they would have been rescued by a boat. So, what happened on the island that once again caused time to speed up? It seems kind of strange that time could move so quickly on the island, especially since it was still day time and it never showed any sort of changes like the sun or clouds moving.