Edward Gibbon kept a card catalogue of his books. 1600 of the cards survive. They may seem odd from today's perspective, as they really are playing cards. In the early days, playing cards were printed with the back sides left blank. This side could therefore be used to record information. Gibbon used it for bibliographical information, but there were other such uses that could benefit from a uniform format.
Some people claim that card catalogues was invented in France during the French Revolution because, according to an edict of May 15, 1791, all the titles of books that were confiscated from the church or from citizens were to be recorded on the blank side of playing cards. This is almost certainly false, as Burke's (playing) card catalogue predates this edict by a number of years. There are earlier recorded uses. Jean-Pierre Bergeret proposed in 1763 that the principles of botany he proposed could be written on the back of "fewer than twelve playing cards."[1} A Dr John Morgan at the College of Philadelphia advertised in 1765 a course on medicine on playing cards. And Jean-Jacques Rosseau apparently wrote his Reveries of a Solitary Walker "between 1776 and 1778 from notes on palying cards taken while he was walking. And there is more ...
1. See See Simon Werrett The Afterlife of Useful Things: Recycling in the Long Eighteenth Century, ed. Arianne Fennetaux et al. (London: Routledge, 2014). There is, of course, no guarantee that the cards were "recycled." Some decks were bought for the explicit purpose of taking notes or making bibliographies.
2. Simon Werrett, "Recycling in Early Modern Science," British Journal for the History of Science 46 (2013), pp 627-646, p. 634.
"When Rousseau died in July 1778, the unfinished manuscript of Reveries was discovered along with the 27 playing cards on which Rousseau had jotted down his thoughts while walking. He had been working on the 10 'Walks' that comprise Reveries until three months before he died. "I am devoting my last days to studying myself," he wrote (from The Guardian). Rousseau is also mentioned by Werrett. See also here, and, for Gibbon, here and there.