One of the cool features of the Nexus 7 that isn't fully explored in the included documentation is USB OTG or 'On-The-Go' and the ability to use a USB OTG adapter. Now an OTG adapter is basically a female micro-USB connector that plugs into the micro-USB connector of your Nexus 7 and provides a full-sized USB 2.0 or 3.0 connector on the other end. You can then plug this into a 'hub' which can provide multiple USB connectors so you can hook up multiple different USB devices to use with your tablet. Even better these connections are actually powered by your Nexus 7 so you don't need separate power for each device connected making it perfect for mobile use.
Now the variety of devices that will work with your Nexus 7 and a USB OTG cable and/or hub is actually pretty impressive and includes keyboards, mice, game controllers, USB-to-ethernet adapters and certain proprietary devices like a DSLR Remote control Android app. What doesn't work with the Nexus 7 without a little work however are mass storage devices such as USB sticks, card readers or external hard drives of any sort. This can be rectified however by installing the app 'StickMount' which we've linked below although keep in mind this does require root access to your device.
Once your device is rooted and 'StickMount' is installed you can use USB drives and card readers to easily move large files to and from your Nexus 7. You'll want to use a file management and explorer app like ES File Explorer
to find and select your files. You can stream movies and music directly from the USB mounted drive to your Nexus 7 so in essence it becomes a mobile hard drive that you can take with you and your Nexus 7 anywhere. For those interested in exploring this functionality you can pick up one of a variety of Nexus 7 Compatible USB OTG Adapters On Amazon
and we've also linked two 'how to' sources below, CNET's 'How To' section and a video made by tech guru 'Reverand Kyle'.