Detritus in old books

This afternoon a used copy of Roger Angell's Season Ticket (1988) that I ordered came in the mail. In it was an old bookmark from "Books Inc. Since 1851" located in the Stanford Shopping Center, no city or state listed. Also, there was a postcard with a picture of a ballgame at Fenway Park and the words "Red Sox" at the bottom left along with their sock logo. The message field of the card is blank, but it is addressed to a Brian Harwell in Bogota, Colombia. No return address.

I always used to throw away whatever leavings were in old books that I acquired, but lately have been keeping them. I find them to be interesting pieces of the books' histories. A few months ago I found an Eastern Airlines ticket stub from 1983 or '84 in a chess book I purchased, and about a year ago there was a Book-of-the-Month-Club invoice in a Doris Lessing novel. I've also found old, sometimes almost disintegrated, store receipts in a number of used books (the only one I remember specifically from recent times was in Ludek Pachmann's autobiography; it was bought at Brentano's, I forget which branch). It's always interesting to see where the original owner purchased a book, and for how much.