Throughout the OT Chewbacca always wears his bandolier belt from the left shoulder to the right hip but in this one scene on the skiff on their way to the sarlacc pit, Chewbacca has it worn in reverse from the right shoulder to the left hip until they arrive at the sarlacc pit and its back to its original position indicating that during this scene these shots were flipped.

NOTE: If the shots in the above scene were flipped then there is a possibility that the theatrical shot below might have been flipped also.

In the shot when Jabba pulls Leia toward him saying “Soon you will learn to appreciate me”, Jabba’s drink is on the other hand and Carrie Fisher’s birthmark which normally is on the right side of her back is shown on the left showing that this shot was flipped.

When Luke is on the plank he nods to Lando who’s standing to his right then when Jabba says “Put him in”, in the shot of the Weequay forcing him off the plank Lando is suddenly shown on the left side of the skiff. Then when Luke jumps in the air, reclaims his lightsaber, and fights the guards, Lando is shown on the right side of the skiff again showing that the shot of the Weequay forcing Luke off the plank was flipped.
https://www.youtube.com/watch?v=nAnkFVaKnec&t=2m32s

When Boba Fett lands on the skiff and aims his blaster at Luke, the muzzle starts to explode one frame before Luke even strikes it with his lightsaber.

When Luke goes to jump from one skiff to another, you can see that his lightsaber is no longer glowing but is holding a stunt prop instead.

This one has always bugged me whenever I watched the film.
When Vader is lifting the Emperor right when he’s going to throw him into the shaft, you can clearly see that its a fake dummy being thrown.
https://www.youtube.com/watch?v=lbbG02LB7g0&t=1m54s