I have Wikipedia that fits in my hand.
The world is an amazing place that so much information can be contained in such a small volume. A free open source project called XOWA allows you to download Wikipedia’s official backups (available through torrent) and use them as an offline Wikipedia. The size for en.wikipedia.org is about 120GB including images.
If ever the world was destroyed, rest assured I have a copy of an overview of the world’s knowledge on some important subjects (and many useless subjects). Water purification, and crop rotation should come in handy immediately. We can get back to quantum theory when the world is back on its feet.
Why this is relevant is that my entire photo collection is also backed up on the same drive and takes up more space. So much knowledge and information in such a small container. It would be a shame if it were lost.
Storage is cheap, back up everything. Then buy another drive, back it all up again and give the drive to a friend, family member, or safety deposit box for safe keeping. You never know when something catastrophic will happen and all you’ll have is your photo backups… And your copy of Wikipedia.