Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
The ability to carry around a Linux distribution in your pocket has been available for some time with the advent of so-called "Live CDs," which are Linux distributions that run entirely from a CD-ROM. The availability of such distributions, like Knoppix, is invaluable from a recovery standpoint and just plain cool from a geek standpoint.
With the cheap availability of USB keychain drives, running Linux off of a USB keychain makes carrying around a recovery installation even easier. While they are more expensive than a CD-ROM, USB keychains are a fraction of the size.
There are a few distributions that will run from CD-ROM or a USB keychain device; one is SLAX.