Dorothy's apron appears between shots in the beginning of the movie when Dorothy is trying to convince Aunt Em to let her off work so she can go to her audition.
The Wicked Witch of the West's hat disappears after she comes in from the balcony.
Towards the end, as Dorothy and Co leave the stage, the Wiz is holding his hand out to shake hands, and in the close up shot he has taken his specs off. When we zoom out, and Toto says something to him, he is still wearing his glasses.