This is a question I sometimes wonder about, but haven't found an answer. Libraries deal with this issue, sometimes called digital preservation. A data dump is below; I've collected the info with the idea of looking into it later.
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RESOURCES
Here are a few resources I've come across, planning to look into it in detail in the future. Unfortunately, most resources seem to be written for experts in institutions, who have different needs and resources than you and I:
* Library of Congress: http://digitalpreservation.gov/
* APARSEN (Europe): http://www.alliancepermanentaccess.org/index.php/about-apars...
* British Library: http://www.bl.uk/aboutus/stratpolprog/collectioncare/digital...
* OCLC, a major library (consortium? association?), should be a good resource.
* The Internet Archive might be a good resource.
* OAIS (Open Archival Information System) is a solution with at least some institutional users or interest, including NASA and OCLC.
* Article: A balancing act: The ideal and the realistic in developing Dryad’s preservation policy by Sara Mannheimer in First Monday: Dryad is a scientific data long-term repository: http://firstmonday.org/ojs/index.php/fm/article/view/5415/41...
* Article: "Your Personal Archiving Project: Where Do You Start?" in a Library of Congress blog: https://blogs.loc.gov/thesignal/2016/05/how-to-begin-a-perso...
* Book: Moving Theory into Practice: Digital Imaging for Libraries and Archives Research Libraries Group, 2000: Apparently well-respected book; widely referenced in my brief searches. Outdated?
* HN discussion: https://news.ycombinator.com/item?id=7842629
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FORMATS
Let's start with: What formats are recommended for long-term preservation? Some specs would be:
* 100% fidelity: But to what? The same Word document can appear differently on different current systems
* Compatibility with systems 50-100 years from now
* Metadata handling
* Organization: Relationships between different objects, e.g., photos from the same vacation, maintained
* Solution for dynamic or interactive data
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SYSTEMS
Some specs for the preservation system:
* Periodic fidelity and functionality check: Don't just turn on the system 25 years later and think it will work and the data is uncorrupted.
* Redundancy
* Compatibility with systems 100 years from now, likely including a reliable upgrade path.
* Migration path to new hardware as old hardware becomes unavailable
* Availability after the owner dies
* Confidentiality: Your whole life will be there, and consider that other people's personal information likely will also be in the archive