What is a run book?

A run book is the document that lets someone who is not you get the business working again:

• It lists the systems you depend on and who the provider is for each.
• It records how to get in - not the passwords themselves, but where they live and who can reach them.
• It names the humans - the accountant, the IT contact, the insurer, with numbers that work outside business hours.
• It is stored somewhere reachable when the office and the main laptop are not.

Test it the honest way: hand it to someone else and ask them to log in to one system without your help.