Although flash drives are generally used to access files from any computer, they can also be used to keep a portable program on hand to be used with multiple computers. If you are looking to have a portable copy of iTunes, you'll find that installing iTunes on a flash drive is the best way of doing this. Installing iTunes on a flash drive merely requires selecting the correct destination directory during the installation process.
Download iTunes by visiting Apple.com/itunes.
Connect your flash drive to the computer's USB port.
Double-click the iTunes installation file to launch the iTunes installation wizard. Click "Next."
Click the button next to "I accept the terms in the license agreement." Click "Next."
Click the "Change…" button next to "Destination Folder."
Click the drop-down menu under "Look In:" and select your flash drive as the destination for your iTunes installation. Click "OK."
Click "Install" to begin installing iTunes on your flash drive. Click "Yes" when asked if you want to allow iTunes to make changes to the computer.
Click "Finish" to complete the process of installing iTunes on your flash drive.