What are Nick Allen's favorite music and book in Andrew Clements' Frindle?

There are no direct references to Nick Allen's favorite book or music in Andrew Clements' Findle. However, we certainly do learn that Nick loves both music and reading in general.

When Nick first begins forming his idea to invent a new word, he reflects that he invented his own word as a toddler. When he was a toddler, his mother "bought him one of those unbreakable cassette players and a bunch of sing-along tapes"; Nick absolutely loved every single tape and "played them over and over and over and over" (p. 32). Whenever he wanted either one of his parents or his big brother to play a tape for him, he would say, "Gwagala, gwagala, gwagala" because he didn't know the word music (p. 32). Therefore, gwagala became the word he invented himself to mean music. Later, once he entered preschool, he realized he would need to start calling music by its actual name if he wanted people to understand what he was talking about. This little story shows us that Nick is a very creative person, creative enough to think of solutions to his own problems such as inventing his own word for music to express himself. Not only that, it shows us that he developed a love of music starting at a very young age.

While describing Nick's research for his report on the origins of words and the development of the dictionary, the narrator explains how much Nick loves words and reading, though Nick never looks at dictionaries:

He liked words a lot, and he was good at using them. (p. 14)

Instead of using dictionaries, he felt he expanded his vocabulary "just by reading, and he read all of the time" (p. 14). This passage tells us that, though still too young to appreciate the dictionary as a valuable tool, he already values words and reading. By the end of the story, he has come to value the dictionary because he has come to see how even the dictionary can be influenced by creative thought. Therefore, the reader might deduce that if he has come to value one book above all others, it might be the dictionary, just as the dictionary is Mrs. Granger's favorite book.