Our favorite homeschool resources:
Some years we have used curricula. Some we have not. That's the flexibility you own with notebooking! :)
An awesome reference book for what to study is The Checklist (see homeschool resource list). Of course your state may have particular guidelines you need to follow. In my state, there are not many.
For history, I like to use a spine book that gives us a flow through history. I try to find a book that's not too "textbooky". We will read selections from that spine each week and then choose additional literature books and resource books depending on what topics/eras the kids want to pursue deeper (the curricula listed provided great lists of books).
For science in K-8, we sometimes choose a science book like the ones listed on the homeschool resource list (maybe read the entire book that year or just choose chapters that appeal to the kids). If not following a particular science book, the kids will pick a topic to study on their own and use library books, videos, internet to research.
For high school science, we primarily use the Apologia high school science books. It's difficult to find interesting (engaging) high school level books to study topic by topic.
We use the Handbook of Nature Study and various field guides to help with nature study.
For language arts in elementary grades, we use the Spaulding method to teach spelling and reading (see homeschool resource list). We cover the basics of grammar ... punctuation, capitalization, and sentence structure. These are practiced through their notebooking. We also build a notebook with their new words, spelling rules and grammar rules as we learn them.
For language arts 7-12, we do use curricula to help teach grammar and writing skills. Our favorites are listed in the resource list. I use those resources to teach the skills, but the kids choose topics from their studies for the actual writing "assignments" and these are added to their notebooks.