Multiply a USB drive in as many clones as you like, with ImageUSB
ImageUSB is a free, easy to use and efficient program that will let you create any number of identical USB drives using an image.
The program supports exact-bit copying to reproduce a USB accurately en mass. You can use also ImageUSB to arm a USB drive with OSFClone, in case you are after drive analysis and diagnosis.
ImageUSB keeps the Master Boot Record and any feature of the disk that is cloned.
Precisely because the program is after exact duplicates, any extra space available in the target drive will be left unused as if it did not exist! If the target drive isn’t of the same size, when you finish your job you should format it again to claim all the available space.