I use this from ravpower. You can play your videos and music from the drive using the ipad/iphone app or an app you choose on your device (I prefer vlc for videos). Its an easy way for me to play music on different devices (no wifi on the train). So far the only file I cannot put on this drive are epubs. It requires the iPlugmate app on your device. I hope this makes sense. I am new to the ipad world and I love it so far!
https://www.amazon.ca/RAVPower-Ligh...0933741&sr=8-1&keywords=ravpower+iphone+drive
I also been using the RAVPower FileHub for a long time and it is excellent. I generally use it with a 4TB HDD.
I also have the Meenova Dash-i Plus that works quite well:
http://www.meenova.com/st/p/dash_i.html
At $40, both devices are well worth it.