Possible to have USB automatically update from folder

So I have some files that I keep on a USB. It's just a last resort backup of my most vital files on my computer. I update it every so often, adding different files to different sub folders of sub folders, so currently the most time efficient way is to just delete the files on the USB & move the folder I keep everything under to it again (around 100 gb). I was wondering if there was a way that I could set it up where it automatically updates the drive once I've put in the password? I have a 15 MBP Retina & it's running Sierra. Any help would be greatly appreciated.