Ask HN: How to do business continuity as a one man band

I'm an independent software engineer, I've got a few clients who rely on me for their websites and internal systems (small bespoke CRM /ERP type things).

If I got run over tomorrow, how could they not be affected? Everything's backed up and source code is in Git etc. It's more all the processes (deployment etc) and all the credentials that come along with that. Obviously I can document the process, provide them with regular copies of the database backup and dumps of the source for each release, but what about all the other bits?

What are other small shops do in terms of business continuity for their clients? How do you manage it?