Depends on what you want to accomplish.

I assume you mean tou do not have Internet access, but have some ability to do wireless networking - e.g. ad-hoc wireless networks or use a mobile WiFi hotspot. 

For archaeological field work we have set up battery / solar operated wireless routers and a server ( e.g. a laptop ) which allows mobile devices to collect data and post it to the server.   So it all comes down to what sort of situations do you want to hedge against.

To be honest the "best" way we have approached this is using a file synching process.  The mobile application persists its data as individual files. So you have a copy of everything ON the device itself.

A file sync client syncs the data from the other devices to each other - making multiple copies.   This may require different types of devices than you want to use.   However one situation which works well is:

You have several identical, cheap laptops / sub notebooks / etc form factor devices.   Each device participates in an adhoc WiFi network.    You have a Data folder, with a subfolders for each device, say "Logger1" thru "Logger6"  and you use RSYNC to do a unidirectional sync from each laptop to the others.

So you drop a new data file on your local drive and it is synced to all the other devices as network access permits.

Using of network sharing or trying to build out a shared files system - these rely on stable networks.   Which you don't have.   Also storing the data in a structured database is antithetical to synchronization as well - in that case you would either need to update multiple database instances - which is tricky.

IDK how much control you have over the applications or devices - but this is the way I have engineered thing from scratch - and it works.

Hi there

A raspberry Pi with a bluetooth connection. The phone can send its files to the portable Raspberry Pi mini-server when every they are in the range. The Pi can save the data in a database in the SD card

Hi

You can use wireless sensor network. Or a simple raspberry pi configured with MQTT and IFTT through a broker server. It can send the data to your email or/ and phone

I suppose that downloading data by ordinary USB wire from mobile device (e.g.tablet) to PC is adequate answer to your question. It will be simillar as download photo from mobile device. Maybe is possible use SD card as target storage in mobile device and replace it to notebook.