Travelling and storing GO-PRO files without a laptop

[Neil]

What are your objectives of the film?
How long you going for?
Why aren't you carrying a laptop?

I personally advise you to film at the best quality that is available at the time. So that future generations can enjoy what you did instead of making them suffer it.

However, I will also keenly point out that filming hours on end will really be a crap product in the end. Make a swatch of the experiences not trying film the whole experience and nobody got no time fo'dat! Learning from people who make good videos that I know, usually filming for 10-30 seconds at a time of vistas pretty much will cover you on the helmet cam angles. Unless you're narrating or doing something detailed that people might want to watch.

While it was suggested that OTG products exist, frankly they kill battery life of your phone/tablet and depending on the unit might not support the OTG device. So be aware of it. I have a unit that works great with my Samsung Galaxy S5 and allows me to stream 1080p to a screen for movies allows me to read cards and so on. Note that even with a charger plugged in the power consumption exceeds the charge supply.
Whlie there are products available on ebay like these: How do I Transfer Files USB to USB - Working with computer files and best data backup methods you might struggle to get some reliability out of them.

Good luck, having a couple of SDs is recommendable as time to time cards do fail.