In my previous house, the previous owners left a folder with information about various known quirks, which came in handy. They also left a manuals for things like the stove and fireplace, as well as contact info for contractors they had used over the years. It ended up being a sort of owner’s manual for the house that we really appreciated. We did the same when we moved out.

My current house… There’s an under-cabinet CD player/radio in the kitchen that I almost never use, and the previous owners left the soundtrack to the Trolls movie in it, so I guess there’s that?