imo: 2,9,11,12,14,16,17,24,25,28,31,32,34,35 except that last page,36,37,38,39,40,41,42,44,47
Some of these are mildly referenced in other books("Remember that cat from book 2?"), but I feel like none of them advance the story or any of the characters in meaningful way.
That said, I still think 24 is ***ing hilarious.