The precise origin of what we call a book (loose writing sheets bound on one edge) is lost in time.
Books or codices are older than we think, but it’s not till the age of writing on papyrus in ancient Egypt that we get something that closely resembles our modern book. The thin papyrus could be bound into a codex (book) more easily than wooden tablets and that’s what the Egyptians did. Papyrus was abundant and cheap so these papyrus codices were the very first notebooks. They were used to keep informal notes and scribbles by the technologically savvy ancient Egyptian.
The serious written material, however, was still scrawled on scrolls that filled libraries many centuries into the Common Era. Long before then, a rivalry between libraries would push forward the development of the book. The great Library of Alexandria in Egypt was in a tussle with the Library of Pergamum, a young upstart library in Turkey, a century younger but competing viciously for all the best scholars of the time.
Both libraries housed hundreds of thousands of scrolls of papyrus, which was only produced in Egypt, so the Egyptian king stopped the export of papyrus to Pergamon. Not to be defeated, the Pergemenese worked with animal hide and invented a new writing material, parchment.
More expensive than papyrus, parchment was precious and could not be wasted on mere scribbles. So old parchment pages and documents were reused by scraping away the ink from the surface or by washing them with milk and oat bran. Be thankful this is not how you need to clear space on your phone or tablet.
Parchment books continued a thousand year reign as the only notebooks of choice. Paper wouldn’t take over the Western world until the 12th – 14th centuries CE, and then at last people could stop scraping their embarrassing journal pages clear or washing them in milk. By then there were new erasing technologies available, but that’s a different chapter in the story of stationery and breakfast.