It's an old expression actually originating from a peg, with the Rooter being the snout, and the Tooter being the tail. So basically it means the whole hog from snout to tail. But has come to mean from head to toe.
A small piece of information. Derived from the word ken, used often in the scottish language and is synonymous with knowledge.
Person 1: "Hey I don't get this shit. How do you solve this problem?"
Person 2: "I got that one. Give me some kenlets on this assignment and I'll help you w/ that one."