Just as a completely opposite example, if you do not have large amounts, you can copy from one card to the other in camera. If the XQD is your main card, buy a few slow, cheap, big CF cards, and you can back up directly (if slowly) to them in the camera, requiring nothing at all in the field except battery power.
Obviously not practical for hundreds and hundreds of gigabytes. But a thought for "minimalist" situations.
I carry a laptop and a USB drive, and make copy on each before erasing and reusing the cards, when I am on a long trip.