I've tried various methods to get 10+ live cds such as Parted Magic, Knoppix, Systemrescue, Backtrack, Ultimate Boot CD, and Hirens boot cd all on one usb drive. Check out LiveUSB Multiboot, a fairly easy way to boot those iso's. It uses grub to boot everything and is serious killer app. There are a few weird dependencies like xterm but once installed it works like a dream. The website is in french so you'll need google translate or something. It's nice to have all those tools in one place. Also check out my post on DriveDroid for android which does the job in a different way.