The things to talk about in this matter have little to do with electronic book readers becuase as the ducks illustrated your electronic books are simply another folder and the ducks is exactly correct. The more important matters, in my opinion that need to be discussed here are not the electronic books but what hardware and software to use to do the backup your your books with.
A jump drive is better known among IT folks as a USB drive since it attachs to your USB port. My recommendation is not to use a USB drive, I would recommend that you go out and buy an external hard drive that also attaches to your USB port. The reason for this is, see for yourself, the cost per megabyte of the drive. The external drive costs a lot less in terms of dollars per space on the drive and stays permenantly attached to your drive and gets t he backup done without intervention from you. My recommendation is for the largest external hard drive that you can afford to purchase. There are two types of external hard drives and the one that you buy depends on what you will be doing with the backups. There is a desktop version and a portable version. The difference mainly is that the portable gets all of its electricity from the USB port on your PC while the desktop version has a seperate power plug. Use the desktop version for weekly and monthly backups. Use the portable version for off site backups.
There is little difference in the quality of the drives, iomega, segate and western digital all make quality products so I would recommend that you chose the cheapest from the cheapest re-seller rather than a particular brand. The cheapest that I can find at the moment is a $70 1TB (Terabyte) Craigo drive at Amazon. 1TB is going to be so huge that I would dare say that most people here can't read that much in their life times.
As for portable external hard drives Amazon has a 1tb segate for $90, so there is little price difference between the desktop and portable versions so go for the one that makes most sense for you.
Beyond the hardware issue there is the software issue, what software will you use to get the job done. Here the dominant software is Symantec's Norton Ghost which sells for $37.60 by software media.com so thats rather cheap. If price is a concern then there is Migo digital backup premium for $9 from TechforLess.com.
In my mind this is really what you need not the drive that you were talking about earlier.