Background: I am a programmer that occasionally has access to other computers when on vacation or something. These are generally the machines of friends or family, so randomly installing Ubuntu on it wouldn't be terribly polite. I would like to completely avoid the hard drive of the target machine.

Not all of these machines can boot to USB either, so that simple solution is out.

What I want to be able to do is boot to an Ubuntu live CD, plug in a USB drive and then grab various updates and other applications, installing them to the USB drive.

Later, on another machine, put in the live CD, after boot, put in the USB drive and then magic, I have all of the updates/applications/data/etc that I've tossed onto the drive.

I suspect that it should be possible to mount /home, /var, /usr, and maybe a couple of other locations from the USB drive or something along those lines.

So is this possible and what do I need to do?