This looks cool: GlobeTrotter [archive.org] is a 40 GB external USB hard drive that comes pre-installed with Mandrake Linux. Basically you can carry it around and temporarily turn any computer into your Linux box!
It should be more flexible (and run faster) than CD-based distributions like Knoppix or Mandrake Move [archive.org], although it’s bulkier than carrying a CD and a keychain.
Hmm, I wonder if I could get Damn Small Linux to boot off a USB keychain…
