I would include a personal diary: writings of what it is like to live today. The Holy Spirit once told me, "500 years from now, history will be taught by the study of diaries written by people who lived during the era."
Because history is so dramatically distorted by those who hold power, and academia has become a major tool for "socialization", text books will be abandoned for the raw material.
Also, you could compile a list of prophecies. It will be interesting for people of the future to see what failed and what came to pass!