Lies and Imagination 1: Holden, in his wish to "feel some kind of good-by" (pg. 16) before he leaves Pencey, shows himself to be concerned with the authenticity of his own feelings. He wants to use his imagination to feel more connected to the world and to his own emotions.
Lies and Imagination 2: Holden's inability to stay enrolled in school isn't a result of a lack of imagination--he's a fan of good books and seems interested in learning from them. It's almost as if he has too much imagination for school. Though it's never directly said, we can assume from his performance on his essay test about the Ancient Egyptians that he loses patience with activities that don't seem to have a point and don't stimulate his imagination.
Lies and Imagination 3: The report Holden writes for Stradlater about his brother Allie's baseball mitt, shows that Holden has a poetic imagination. Stradlater, who in all likelihood is not particularly poetic or imaginative, criticizes the report because a baseball mitt seems a pointless thing to describe.
Lies and Imagination 4: A big part of Holden's trouble with movies is that they pollute peoples' imaginations. Holden seems to feel this is happening to him when he feels compelled to act like a movie character, gripping his side as if he's been shot, for example.
Lies and Imagination 5: Holden's imagination isn't used just in the service of fantasies and escapism. When he's led to think about war after watching a war movie, he shows that he can also use this imagination to explore some issues with which he hasn't had any personal experience.
Lies and Imagination 6: When Holden finally makes it to the Central Park lagoon to look for the ducks, he finds no evidence there to settle his curiosity about what these ducks do in the wintertime. This recurring concern about the ducks seems to be symbolic of Holden's desire for purpose and direction.