If you have access the device running Node-RED, then a minimal backup would be to copy the files:
~/.node-red/package.json- your flow and credential files (check the Node-RED startup log to get the exact filename)
- your settings file:
~/.node-red/settings.js
If you have not set the credentialSecret property in your settings file (there's a big message in the log on startup telling you to if you haven't), then you'll also need to copy the value of _credentialSecret out of ~/.config.runtime.json (or .config.json if on Node-RED 1.1 or earlier).
For the majority of cases, that would get you everything you needed to restore your flows elsewhere.
If you don't have access to the device running Node-RED, then you will be able to export your flows as JSON from the editor, but it will not include an credentials. You'll also have to take a manual record of the extra nodes you have installed.
