I came across a good site with some history of the origins of the word Caddy or Caddie.
The records are not certain, but historians believe that Mary, Queen of Scots, came up with the term "caddie" in the late 16th century. Mary grew up in France where military cadets carried golf clubs for royalty. It is possible that Mary brought the custom to Scotland, where the term evolved into the word "caddie." Alternatively, the word "caddie" may have originated from the Malay word 'kati'.
Kati is a measure for tea leaves and is printed on boxes used to carry and collect the tea leaves, hence its use in terms reflecting carrying and collecting.
Also, the word may have originated from the Welsh term "cad", which is a "battle", "contest", or "test", such as the Cad Goddeau.