How can I keep multiple live/bootable ISO images on a single USB drive?

"This is an interesting question. I can see it being very useful to have a single USB ""master"" LiveCD, instead of having so many different DVDs and pen-drives scattered around.

There seem to be a number of different approaches to this, all of them doable:

Mk-boot-usb: a Script to Create Multiple-Bootable USB Sticks
Boot Multiple Distro from USB / Flash drive / Pendrive
Booting multiple LiveCD's from a single USB stick"

"A hard disk drive enclosure made by Zalman was made for exactly this purpose. It is named ZM VE200 (USB 2.0), ZM VE300 or ZM VE400 (USB 3.0). I use it on a daily basis to test laptop computers I repair. I've never been disappointed by it, but only by some old BIOS that prevent the laptop to boot from external devices and USB port that do not supply enough juice.

With an HDD formatted with NTFS or FAT inside and with a directory named ""_iso"" where you write ISO files, you are then able to boot from this external hard disk as if it was an external CDROM. It simulates an external optical disk drive with the right ISO in it .. fortunately you do not have to burn.

The product page best explains its purposes:
http://www.zalman.co.kr/eng/product/Product_Read.php?Idx=674

My experience with this is quite good. I used to burn a lot of CDROM before buying this useful gadget. Now, I just collect ISO files in the right folder, all on the same device:

GNU/Linux distributions (installers and rescue cdrom as System Rescue CD)
Hard disk drive diagnostics tools
Motherboard firmware flasher
SSD firmware updater
Microsoft Windows PE
Ultimate boot http://www.ultimatebootcd.com/
Plop boot manager http://www.plop.at/en/bootmanager/index.html

The only thing to check is the power consumption of the hard disk drive you put in it. But that's a common thing to look at when you deal with external hard drives."