To keep the kids occupied on long card journeys, I use a travel router and a portable hard drive to feed movies to the kids tablets. The router I use is discontinued but works as a DLNA server which can be picked up by many media players once connected to that wifi network.
Something like this would work if you want a truly portable solution;
https://www.amazon.co.uk/dp/B00VBAE5..._5yj-DbTWNV992
Very useful when travelling too if hotel Wifi is slow or you pay per device as you can connect wired and it acts as a wifi bridge