cracker-jack n.

also crackerjack, "something excellent," 1893, U.S. colloquialism, apparently a fanciful construction, earliest use in reference to racing horses. The caramel-coated popcorn-and-peanuts confection was said to have been introduced at the World's Columbian Exposition (1893). Supposedly a salesman gave it the name when he tasted some and said, "That's a cracker-jack," using the then-popular expression. Compare cracker (n.1). The name was trademarked 1896. The "Prize in Every Box" was introduced 1912.

"Your brother Bob is traveling, isn't he?"

"Yep. He's with one of the big racing teams. I tell you, he's a cracker-jack! Wins a bushel of diamonds and gold cups every week."

[Life magazine, Aug. 1, 1895]