One of the most useful tools to have on a USB drive can be operating system install files.
Plug in the (larger-than-2GB) USB drive and back up its contents (unless you don't care).
Begin downloading this .iso from the official Ubuntu source.
If in Linux run in terminal:
sudo apt-get install usb-creator-gtk
(In Windows, install a USB OS boot tool from online)
Once all files are ready, run the usb-creator and load the .iso and the USB drive should be ready for use.