Ask HN: What tech knowledge to back up?

Everything going on in the US right now is really concerning, including a theory that the US will implement a "great firewall" similar to what's used by countries like China and Russia.

Information on how to use tech considered subversive may be hard to access in the future. Guides like how to get around firewalls, or how to access and use specific software or information hubs might be altered or restricted.

What tech knowledge do you think should be stored offline? What knowledge is likely to be restricted in the future?