The goal behind this is to stash vitally important information necessary for the re-establishment of a free and prosperous society. Again, I don't think a new dark ages is likely, but it is a small possibility now, and it is easier to prepare for it now then to try and stuff some random books into a safe and bury it later.
Ideally the information would be laser etched into metal plates and dozens of copies buried around the world. Gold would be the ideal material as it doesn't corrode over time, but stainless steel might be better as it has relatively little value.
Laser etching allows us to write very small, we could even include a magnifying glass to make it easier to read.
The first section might have to be a language tutorial, because we just don't know how language will change. Best to make it easy for those who come later. Reminder to self: talk to people who have translated ancient dead languages and what would make it easier for someone to do it if we do it deliberately.
The second section might be about government. While it would be tempting to give them just the Constitution it might be better to go a similar route the founders took of the major documents of the Enlightenment and let them figure it out for themselves. With some lessons learned essays as well.
The third section would be about science and technology. While I doubt we would regress to the Stone Age it is probably better not to take chances and give more information then less. Detailed instructions from stone knives and bearskins to steam engines, transistors and space flight. This will take a lot of research and probably will need to be focused and a lot of help.
I am beginning to wonder if a wiki might be a better way of doing this. I need help on this and a blog probably isn't the best way to do it. But I have to start somewhere, and this is as good a place as any.