Best way for two Unity android apps to communicate?

I’m making a cardboard app that requires a bunch of settings and parameters. I want to make an admin app that will be non-cardboard and allow the user to set all the variables. Whats the best way to share settings between these two apps?

Thanks.

some ideas:
could save/load settings to sdcard,
save data to server and fetch from server,
start cardboard app from the settings app and pass some parameters (and save those to main app),
or have non-vr mode in the start menu/settings…

Save/load settings to SD card is probably the easiest. Thanks!