The string is for pulling up the heel strap in the back of the boot. You
can substitute any number of things - a shoe-lace, bailing twine, a piece of
leather latigo. What works best is a 1" wide strip of nylon webbing. I
have a two foot piece that goes in my saddle pack with the boot, it's fairly
inexpensive when you buy it by the yard at a fabric store. Just burn the
ends so it doesn't fray and you're in business.
in Gardnerville who remembered to put the "t" in this time <g>