StickMount is a root app made by the famous Chainfire that allows you to mount storage over USB. While Nexus devices lack microSD cards, you can add storage by using a USB OTG cable and adding storage with USB media.You plug a USB drive into the OTG cable, plug the cable into your device, and use StickMount to mount and use it. It’s a simple, if not a little bulky, way to add storage to a device.
The app was rendered useless after the Android 4.2 update due to some security changes in 4.2, but Chainfire updated it today and it’s fully working. He also introduced a pro version that includes a feature to kill apps preventing unmounting and to trigger a media scan after mounting or unmounting. But it really supports development of this app and many more that Chainfire makes, so it’s worth the $2.49 price tag. Hit the source links to get it!