When Charlie is reading Claire's diary, on one set of pages the letter a is written as the double-storey a often used in printing, and on the next page as its single-storey version, how it is most commonly hand-written.
Walt is lost in the forest looking around him. When panning across the landscape of the forest, a crew member and a portable toilet can be seen on the right side of the screen in behind some bushes. It may only be visible in wide screen.
During one of the flashback scenes, Walt, Susan, and her husband are in their living room in Australia and Susan sits on the couch after feeling light-headed. In the second shot of her on the couch, a blonde crew member is visible in the top right corner of the screen.
When Charlie is reading Claire's diary, the camera pans over one of the pages, which contains the word "realized". Claire is Australian, and Australians spell the word as "realised" per British spelling.
Locke tells Michael that he was giving Walt a pencil to give to him, but Locke is holding a pen, not a pencil.