This is a very cool thread because it has really made me think about the ways to create and transfer files while off line. I came up with a glossary of terms that helps me sort through this stuff: 1) mobile hotspot--allows sharing an internet connection using wifi; 2) travel router--uses usb connection to a flash drive to allow file sharing on a local wireless network 3) bluetooth--allows limited file sharing between certain devices.

You can't use a mobile hotspot for file sharing. It's only for sharing internet. But if you have a travel router (e.g., HooToo Nano) available, you can share gpx, tcx, and fit files from an android phone or tablet to a bike computer. John has suggested using Bluetooth for file sharing. John, you're right! It is possible! Bluetooth can be used for more than connecting keyboards and headphones; however, in my testing, the file types one can transfer are limited to jpg, mp3, and pdf. While workarounds exist for transferring other file types, these require rooting or renaming files on a target android device. These tricks probably won't work with a bike computer. Bottom line: with no online connection whatsoever, I think you're stuck with using the Osmand app for route design and a travel router to transfer the gpx file to a bike computer. While I hope I'm wrong, I just don't see any other easy way to do this.