I have a 2gig voyager that I occasionally use for data moving when I visit my brothers etc., it also contains my passwords.exe fSekrit container, and some various tools (subversion, the putty suite of SSH tools, notepad++ and such). Don't use it that often, but when I do it's a very nice little thing, and obviously it's ultra portable.
I also have an older 128meg drive, with a DOS boot sector - useful for running harddrive diagnostic tools, BIOS flash updates, and playing around with the occasional low-level code that won't work under windows.