Origin of Phrases - C
Cracker jack
Meaning: To be very good at something.
Example: Don't worry about your DUI. We will hire a cracker jack attorney and get you off.
Origin: "Crack" means of superior excellence of ability as in "he's a crack shot" meaning excellent, superb. "Jack" being like "Joe", a common man. "Cracker jack" thus means a Superb man, any man.
Curiously "cracker" is defined as a bragging liar, which is very much in contrast to "cracker jack" which implies someone who delivers.