I like your "prepper" mentality!
If having access to another device without internet is in the scenario I think it would be possible to install the standalone version on an usb stick. Sync it the usual way, just before you leave for travelling.
Just keep an eye on this bug:
JoplinPortable can't update to latest version of plug-ins - Support - Joplin Forum (joplinapp.org)
Other scenario: Export to PDF or md files in bulk, and store this on an encrypted usb stick?
Your "Single File" requirement is another story I think ....