Save human knowledge. When people of this age think about knowledge worth saving, they usually think about belief in the Cartesian mechanical philosophy, that dead matter is the basis of reality, and about techniques for rebuilding and using machines that dominate and separate us from other life. I'd like that knowledge to die forever, but I don't think it works that way. Humans or any other hyper-malleable animal will always be tempted by the Black Arts, by techniques that trade subtle harm for flashy good and feed back into themselves, seducing us into power, corruption, and blindness.

Our descendants will need the intellectual artifacts to avoid this -- artifacts we have barely started to develop even as the Great Bad Example begins to fall. In 200 years, when they are brushing seeds into baskets with their fingers, and a stranger appears with a new threshing machine that will do the same thing with less time and effort, they will need to say something smarter than "the Gods forbid it" or "that is not our Way." They will need the knowledge to say something like:

"Your machine requires the seed to be planted alone and not interspersed with perennials that maintain nitrogen and mineral balance in the soil. And from where will the metal come, and how many trees must be cut down and burned to melt and shape it? And since we cannot build the machine, shall we be dependent on the machine-builders, and give them a portion of our food, which we now keep all for ourselves? Do you not know, clever stranger, that when any biomass is removed from the land, and not recycled back into it, the soil is weakened? And what could we do with our "saved" time, that would be more valuable and pleasurable than gathering the seed by hand, touching and knowing every stalk and every inch of the land that feeds us? Shall we become allies of cold metal that cuts without feeling, turning our hands and eyes to the study of machines and numbers until, severed from the Earth, we nearly destroy it as our ancestors did, making depleted uranium and polychlorinated biphenyls and cadmium batteries that even now make the old cities unfit for living? Go back to your people, and tell them, if they come to conquer us with their machines, we will fight them in ways the Arawaks and Seminoles and Lakota and Hopi and Nez Perce never imagined, because we understand your world better than you do yourself. Tell your people to come to learn."