Source : Webster's Revised Unabridged Dictionary (1913)

Knapsack \Knap"sack`\, n. [D. knapzak; knappen to eat + zak a
   bag. See {Knap}, v. t., and {Sack}.]
   A case of canvas or leather, for carrying on the back a
   soldier's necessaries, or the clothing, etc., of a traveler.

         And each one fills his knapsack or his scrip With some
         rare thing that on the field is found.   --Drayton.

Source : WordNet®

knapsack
     n : a bag carried by a strap on your back or shoulder [syn: {backpack},
          {back pack}, {packsack}, {rucksack}, {haversack}]