I was lucky enough to be on a wonderful island in the middle of the Indian Ocean for a 10 days scuba diving holiday. I had my new GoPro 4 with its very expensive ultra fast 64 GB micro SD card. After the first dives, it became obvious that my card was too small. I had a few old SD cards and some pendrives with me. And a tablet... No laptop or computer. I started copying the files from the 64GB card to the old ones using the tablet memory as support. Moving all those files from the GoPro to the other chips soon became a boring and lenghty nightmare.
Back home, I realized I have a lot of unused old SD cards and USB pendrives that I could still use as back up. It wouldn't be too difficult to create a small tool to move files from/to different memory supports. 2 SD slots, 1 USB and a nice little board as the teensy...
In order to keep it simple and cheap, I decided to make it without wireless connection.