As people on this forum have said for years, "Save your receipts, your owners manual, your window sticker, your original bill of sale, anything that documents the history of the car or makes it a little more special than the rest." as it will add to the luster when it comes time to sell. That all worked for the BaT seller.
I don't have much from my Z other than the original bill of sale. But, for my Porsche 914-6, I have documents from the original, and subsequent, owners as well as an accordion folder full of restoration receipts. All good to have for the next owner. With the Avanti, I have a copy of the original factory production order as well as the six page final assembly line inspection checklist. Best of all, I have hand written letters from the designer, Raymond Loewy, noting the Avanti's VIN. Provenance should probably be spelled Provenan$e.
Dennis