Marginalia is the best! I have a handwritten note about Ayn Rand in my 27 year old copy of Enchridion, a great reminder that she is like chicken pox, better catch her as early as possible. And several books such as I Claudius held together with duct tape. And soy sauce stains in Gargantua and Pantagruel from the place my grad school gf worked. Those count.

A bit of irony, going through old stuff I found a copy of Neal Stephenson's In the Beginning... was the Command Line on top of handwritten running logs from sr yr of college. In that book, there was a ticket stub from the time I was 86ed from an amusement park. (I did not eat enough after training that morning.) I was escorted on a golf cart back to our car where I finished Neal's now charmingly quaint essay with the plastic handle listening to Nirvana.

This was August 2001 and Mac OS X had barely come out. Maybe AI rhymes where Chinese free open-models clean up but someone proprietary figures it out. Which is sad as someone dominant in the ecosystem right now is the equivalent of Gary Kildall.