The strangest thing I ever found in a book wasn’t so much a physical item, it was more of a synchronicity of sorts.
During the 1992 Los Angeles riots, after a jury acquitted the police of beating Rodney King, San Francisco experienced a smaller riot that lasted for six hours or so, resulting in the selected looting of downtown, and the then mayor imposing a curfew and limiting movement for the night.
I remember that I had picked up a copy of Nathanael West's novel "The Day of the Locust" (1939) about a week before the riots. I was downtown when the riots broke out, and I had just gotten to the end of the book when the riots occurred in the story just as they were happening all around me.
If you think that’s strange, it gets even stranger. In the book, the riots occur in Los Angeles during a film premiere and the narrator is surprised because it reminds him of a painting he made titled "The Burning of Los Angeles".