Apparently, a lot. I wrote journal after journal, filled with ideas about my characters, observations on nature, other writers, and big chunks of the novel itself. Here’s a pile of my handwritten pages in Moleskine notebooks.
Then there were the books I read, literally hundreds of books. I would read a biography about a writer describing what they were reading when they were writing their books, and then I’d go read those, too. Novels, literary criticism, books by writers on writing. This is just one shelf in my living room. There are more books in my study. And books on the top shelf of my bedroom closet. Not to mention the ones stacked in chairs, under tables, on the floor.