I've been having fun over the last few days with putting a Linux installation onto the SD card in my phone, so that I can then boot my computer up from it. Just plug the phone into any old PC, reboot, tell it to boot off the USB device, and there you go... all my docs are now stored encrypted on my phone, and I can even mount the encrypted partition directly on the phone if I want so that I can get to the files when I'm on the move. I've been carrying a live USB stick round with me for years, but I might ditch it in favour of just booting straight off the phone.
Full details if you want to try it out:
How to use your Android phone as a Linux live USB stick