Use usb on the go to transfer data from mobile to usb
Yes you can and you'll need a few things for that.
https://play.google.com/store/apps/details?id=net.shajul.usbotg&hl=enor this onehttps://play.google.com/store/apps/details?id=eu.chainfire.stickmount&hl=en
Allow root access and voila, you can transfer data back and forth to your USB.
You can drop by Dallas's tutorial as well in the link below
Or if you own a nexus you can simply download Nexus otg manager. No need of root as well!!!
I don't know if it works on other devices but you can definitely give it a try. Let me know if you want full version of that app.
If you got nexus 4, 5, or 6 with OS Lollipop. No need to root your device. Just simply install ES file explorer from playstore and plugin the otg usb flash drive. Open ES file explorer, tap menu on the left corner, choose local, and the usb will appear and tap it to explore it..