Reply #13: A variety of possible meanings.

[Divernan]

19th century slang which was popularized more recently by the movie Tombstone. Means "I'm the man you're looking for". Nowdays it's usually used as a response to a threat or challenge, as in the movie.
"Who thinks they can beat me?"
"I'm your huckleberry."

I'll be your Huckleberry" was used most recently in the movie Tombstone. Doc Holiday told Johnny Ringo, "I'm your Huckleberry", meaning he would play his game, whatever it was.

Others say it refers to Huckleberry Finn's loyal friendship to Tom Sawyer, i.e., I'm your huckleberry, means I'm your loyal buddy.

Yet others posit:
"Huckleberry" was slang for a rube, a hick, a sucker, someone that a "huckster" separated from their cash, the guy that stepped forward from the crowd to get skinned by the guy at the three-card monte table.
A "Huckleberry" would be plucked of his goods, or like the real berry, picked from the bush. So if one would say; "I'm your Huckleberry." he was saying that he was ready to play whatever game you wanted and, perhaps, the results would not be what you intended.