I was in Fort Lauderdale last weekend, officiating Beach Brawl 2014 (and yes, I'll write a post explaining roller derby, given the number of times it's been requested), and I left my Flash drive in the business center of the hotel. I don't really use it anymore. Once upon a time, Dropbox wasn't as useful as it is now, and you couldn't sync across multiple desktops with simple internet access. You had to go to a web location, upload stuff, and blah blah. It was the same as a Flash drive except less convenient.
So back in the day, I kept EVERYTHING on that Flash drive. And while it doesn't include the most recent draft of my most recent novel, it has everything as of the completion of FAMILY JEWELS. Why? Because Dropbox could get hacked. Accidents happen. It's always good to have a backup of your backups (and I update my external hard drive even less frequently than I do my Flash drive).
This all sounds like sage advice, so what makes this post-worthy? Well, when I first started saving things on my Flash drive, there was no such thing as Kindle Direct Publishing. There was no black market of plagiarized novels self-published to reap what few sales they can from the ill-gotten work of others. Now, if I lose my Flash drive, EVERYTHING on that drive (which is EVERYTHING) could be posted to KDP by a nefarious neerdowell, tarnishing my reputation and stealing my work. While none of those novels have been published, some of them have strong prospects for future revision (Triad Society anyone?). Those prospects are dashed if someone steals them off a lost Flash drive and throws them up on the internet in their current form.
This is NOT to tell you to ditch the Flash drive, but it IS to suggest that you lock any folder that contains your writing. Sure it adds a step for when you want to access it, but adding password encryption means that if you leave your Flash drive in a business center, you don't have to panic and wait to see your first novel from five years ago suddenly shitting all over KDP.
Lesson learned. :)