haversack vs packsaddle

haversack

noun
  • A small, strong bag carried on the back or the shoulder, usually with only one strap, and originally made of canvas. 

packsaddle

noun
  • A saddle designed to secure and carry goods on the back of an animal. 

How often have the words haversack and packsaddle occurred in a corpus of books? (source: Google Ngram Viewer )