Comment by Tepix

What if we want to put something on paper today for it to survive as long as possible?

1-minute research:

Paper: 100% cotton rag or linen rag paper with alkaline reserve. Acid-free and lignin-free.

Ink: Genuine carbon ink applied with a classic dip pen.

Storage: ISO 16245 archival box, Less than 15°C, 30-50% humidity, dark, no oxygen exchange. Always store horizontally. Wear white 100% cotton gloves.

Printing: If you want to print instead of hand-write: Piezography carbon printing or pigment-based inks used by professional desktop photo printers, matte black or photo black ink, printed on digital Fine Art Archival Paper.

Place a single sheet of archival-grade tissue paper or glassine paper between every single page of your document

I think the key is to write something interesting that's worth preserving. That may be the most difficult part.

Any improvements beyond this?