The caboodle in this American expression meaning " the whole lot" is the
same as the word boodle, for "a pile of money", deriving from the Dutch
boedal, " property". The whole kit, of course, means the entire outfit.
The phrase doesn't read " the whole kit and boodle" because Americans like
alliteration in speech and added a "k" sound before boodle in the phrase.
Source: QPB Encyclopedia of Word and Phrase Origins By Robert Hendrickson