If you want to create a backup copy of your Field Maps data, and you have a laptop you have with you, then I would suggest following the first part of Access offline edits from ArcGIS Field Maps directly from an iOS or Android device. You can stop after you've copied your data from within Field Maps to a location on your laptop via iTunes, that's your backup.
If your device ends up destroyed in the river, and you need to extract the data from your backup, then you can follow the rest of the steps in the doc.
A similar workflow exists for backing up data from Quick Capture, and recovering it, if needed. See Export Orphaned Records from an iOS Device.