Original manuals that shipped with your computer. Remarkably nostalgic in a sleeper-kinda way. I bet most people are overlooking this aspect of classic computing.
So much of this vintage peripheral/accessory manual stuff pre-2005 is getting lost or stowed. Even some on websites is lost when companies shut down or back-ups die during moves. If the item is rare it's likely the manual is even more rare.
I have manuals for all my classic gear and you're right. Fun to flip through them once in a while. Especially that big ass Amiga 1000 binder w/ BASIC, how to set up, etc.