There are times when our server (or desktop) goes bonkers and simply refuses to boot up from its HDD. What I usually do is to boot-up from a standard LiveCD and tinker withHDD (and the data). However, it'd be great if you can add all your favorite tools and utilities to a LiveCD to turn it into a full-blown rescue disc.
You can, of course, do a similar thing and create a LiveUSB rescue tool as well. :D