A useful root disk also has to get a root filesystem from somewhere: usually it's compressed on the bootdisk too, and when booted it expands into a ramdisk. I don't think they're easy to make, but there are some available to download.
Apparently tomsrtbt is a well featured boot+root disk... handy in an emergency. http://www.toms.net/rb/
There are others, also LEAF and parted have special purpose boot+root floppies. Knoppix is a pretty complete distro that boots from a CD: http://www.knoppix.org/