You set the bar pretty low. How about knowing where iron ore an coal can be found, and how to refine it into steel? How about gaining access to printed ore survey maps? Maybe you could lay in chemistry, physics, biology, and medical books.
I think a lot about recovering from the ashes, and have some heavy duty books to prove it. It is better to think ahead about recovery than willingly return to the stone ages.
Actually I agree with your perspective. And historically this was the purpose of Monasteries. To preserve knowledge for the future benefit of cultures after a downfall. I think you are right, it is once again time for these knowledge archives to be preserved. But knowing how to work stone and make fire will be the most useful for the general masses as basic general survival knowledge. The curious leaders will seek out the Monasteries and archives to further their knowledge base and then share it with others after the initial downfall.