flash drive to store movies ???

Unfortunately Apple has made storing commercial DVDs to stream from any wireless hard drives or wireless Flash Drives, impossible to do.

You can, probably, store the movies onto an external wireless, Wifi hard drive or wireless, WiFi Flash drives, but you will still have to transfer these movies back to the iDevice in order to play the movie directly on your iDevice.

There had been a work around for this that wireless drive manufacturers were using as a workaround by streaming the commercial DVD movies through Safari on iOS 7 and 8, but Apple coded out/closed down this workaround in iOS 9.

There are ways to circumvent this issue, but we cannot discuss this on Apple supported forums.

Do your own web search about this to get the answers about how to do this, yourself.

As for external drives to use with your iDevices, there are wireless, WiFi enabled hard drives from Seagate or Western Digital and Wireless Wifi enabled USB Flash drives from SanDisk which has, recently, been bought out by Western Digital

Good Luck!

Your signature says you have an iPad 2 and iOS 7.0.4. IF that is still accurate, then yes, MichelPM's post is accurate.

However on newer devices there are lighting flash drives that you can purchase, some which are MFI Certified, that do definitely allow you to store and view movies, photos, files, etc. Obviously you need a lightning connector and iOS 7.1 and higher, so your supported equipment would be iPhone 5 and newer, iPad Air, iPad with Retina display (4th generation), iPad mini with Retina display, iPad mini and newer.

I use one and love it. I travel for work frequently and use it to move files back and forth from work PC to iPad and then back to personal laptop later. And on airplanes, I download my movies onto it and watch directly from the drive, on which ever device I decide to use.

It does use more battery power, so if you're using it to play movies or music all day, you will notice a significant drop in battery.