Since a long time I was looking for a solution to backup photos from my DSLR while travelling. Of course I want to carry as less as possible.
My first solution was my Nexus 7 incl. OTG cable + card reader and a USB stick. This worked good but the main problem here is that you need to have a rooted device which caused several problems to me like wired stuff on Android updates and other stuff. So I decided not to root my device.
My second try was buying a Wifi HDD with built in battery. I decided that 250 GB is enough for nearly any travel. And I found one which is only 60 EUR at Amazon: Intenso Memory 2 Move
Installation is quite easy. Just charge the battery and switch it on. Connect your tablet via Wifi (WPA credentials can be found in the manual) and then you are ready to use it.
The only pitfall I was facing is that I switched the DHCP IP range via the HDD’s web interface without changing the HDD’s IP address itself. In that case the IP address is automatically changed to the IP address to enter as Gateway in the IP configuration.
So for now I really can recommend that as a good solution for backing up your photos.