Live boot CDs have always been the mainstay of security and incident response toolkits. These days CD drives are starting to become scarcer, optical media is prone to scratching, and flash media is rapidly getting cheaper. Additionally flash drives often have much high capacity storage for their size.
As a result USB pendrives are starting to overtake CD/DVD in terms of popularity. One fallback was often the difficulty encountered in getting the drive to both store the required live filesystem and boot from power on. For example, my first successful bootable drive (running BackTrack3) was the result of several days trial and error.
However, things now much simpler thanks to the Unetbootin utility. Simply select a distribution a support distribution from drop-down list which will automate the download of required media and select an attached USB drive and start the process. The tool then goes off in the background and creates a bootable USB drive, no fuss.
Alternatively you can point the utility at a local *.iso file, whilst not all distributions are officially supported by Unetbootin, I’m yet to have it fail on me.
P.S. the Backtrack4 Up and Running video series shows the Unetbootin process in all it’s simplicity.