The Notebook is an item that The Baby Sitters Club members use quite a bit. It is a diary where each BSC member has to write about each sitting job they go on: how the kids behaved, any problems, what happened, etc. Each week, the BSC members have to read each entry so they know what's been going on.
Kristy Thomas came up with the idea for the notebook while sitting for Pinky & Buffy McKeever. While it's not her most popular idea, the rest of the BSC members have to admit it's helpful. Not all of the members like writing in it. The only ones who really enjoy writing about their jobs (and reading about them) is Mallory Pike (who loves writing and reading) and Kristy (because she thought of it).