First, I have enough media cards to cover my travels and then some figuring they are both cheap and that it's cheap insurance to never have to reformat the cards on the road.
For travel back-up, I use a pair of Hyperdrives, one with spinning disk and the second with an SSD. Bought a pair of cases years ago and put in my own drives. They have both SD and CF readers built-in, a small display, rechargeable battery, and can be run off an external AA pack and can be used to transfer to and from your computer. Not much to using them and the peace of mind is priceless.
I've taken them on many week to month long journeys through the years they both seem to work fine and are reliable. Mine are older and had iPad compatibility that I never seemed to use and that model maxed out at 500GB. Newer Hyperdrives don't have this size limit.
When I need to go light, I use my Hyperdrive with SSD and back-up as I go so that I have at least a little redundancy in my files.