I don’t remember my first book, but it must have been a Sooty or Joe 90 Annual (I still have the former, but sadly the latter has long since gone missing).
I lived with my grandparents as a kid and they had kept my father’s Film Fun Annuals from the 1940s. I recall reading the comic-book style stories about Laurel and Hardy, and Abbott and Costello et al.
In fact, Enid Blyton’s books inspired me to write (and illustrate!) my own adventure book as a ten year old: Sand Island!
So while I don’t remember the first book I read, I do remember the first book I wrote, 45 years ago! What about you?