backpack vs kitbag

backpack

noun
  • A similarly placed item containing a parachute or other life-support equipment. 

  • A knapsack, sometimes mounted on a light frame, but always supported by straps, worn on a person’s back for the purpose of carrying things, especially when hiking, or on a student's back when carrying books. 

verb
  • To place or carry (an item or items) in a backpack. 

  • To hike and camp overnight in backcountry with one's gear carried in a backpack. 

  • To engage in low-cost, generally urban, travel with minimal luggage and frugal accommodation. 

kitbag

noun
  • A large cylindrical holdall. 

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