DRMless digital is great - I have a calibre library of thousands - but still more vulnerable.

Canticle of Lebowitz is a great post apocalyptic novel. After the nukes, Catholic monasteries preserve the action tradition of copying down manuscripts. Text doesn’t require any form of infrastructure.

There are also many texts/other media that are not available in any digital format. Obscure or older. For as much of an Information Age we are in, a lot of knowledge is being lost through neglect.