YouTube comments aren't usually the most stirring of threads, but the comments for the famous Doc vs. Johnny Ringo shootout scene has some interesting opinions about what Doc's getting at when he says he's Johnny's "huckleberry." Now you might assume that these mostly revolve around gay panic jokes, or at least old Hannah Barbera references, but they actually boil down into two differing schools of thought: 1) He says "hucklebearer". Huckles are the handles on caskets, and Doc used to provoke men by offering to carry their corpses to the grave. 2) He says "huckleberry", and huckleberries are something you look for.
I'm pretty sure it's "huckleberry", and though I'm not sure about the veracity of any of the YouTube comments, my favorite one comes from Childrenofpwnom: