Create a usb that boots multiple .iso files using MultiSystem 
http://www.pendrivelinux.com/multiboot-create-a-multiboot-usb-from-linux/

With the MultiSystem MultiBoot program, you can load multiple .iso files on a USB flash drive and boot any of them.

The MultiSystem MultiBoot program builds a custom Grub2 menu for your .iso files. It works for .isos such as Ubuntu, Linux Mint, LMDE, PCLinuxOS, Knoppix, Puppy Linux, Pinguy, Bodhi, Zorin, Gparted Live, Grub Rescue Remix, SystemRescueCD and more. It may not work for some other distros, depending on how their .iso files are structured.

Your USB flash drive must be formatted FAT32, with one labeled partition (the label cannot contain any spaces). If you try to use a drive with no partition, MultiSystem will install one and label it "Multisystem".

Installing MultiSystem:
Enter the following commands in a terminal, one at a time.

sudo apt-add-repository 'deb http://liveusb.info/multisystem/depot all main'

wget -q -O - http://liveusb.info/multisystem/depot/multisystem.asc | sudo apt-key add -

sudo apt-get update

sudo apt-get install multisystem
 
In my Mint Cinnamon, MultiSystem appears in the Menu under Accessories.
When the program starts it detects the USB drive, and you can drag .iso files to the small window at the bottom of the MultiSystem screen, or use the disk icon to browse for files.

To delete .iso files from the USB drive, click on the eye icon, on the left side of the window. Then click on the Remove icon on the right.

MultiSystem automatically generates a Grub menu with a menuentry for each .iso you load into it, so you can boot the USB drive and boot any of them.