Upload & Sell: On
I spent 15 days in Africa, where a lot of my trip was hiking.
I considered something like an external drive such as the Hyperdrive, but I didn't want to add another thing to carry, another set of batteries to keep track of/charge, and something else that could break.
I tried the "Backup" mode on the camera, which sounded good in theory. Immediate copies of everything. In practice, though, I was deleting a lot of images each day to make the best use of my cards, and "Backup" mode meant that I needed to delete images twice unless I wanted to waste space.
What I settled on is doing a card-to-card copy a couple times per day during downtime (e.g. lunch, at the campsite at night). That meant I could delete images during the day, pop in my backup card, and do the copy. It also meant that the backup card wasn't in the camera all the time, ensuring that a camera tumbling down a cliff didn't make me lose all the data. I kept enough cards so that I never had to re-use, and brought along two card holders; one to hold the cards I had filled, and one to hold the backups I had created.
If I had to do over again, I'd do it the same way but probably buy a couple giant 128+ GB cards, instead of having to manage so many smaller cards for my backup.
I don't complicate things when I travel. Elaborate rigs that involve phones and external hard drives and wires are a lot of moving parts, batteries, and slowness. I'd either go with a Hyperdrive, or back up in camera.