From WordNet (r) 2.0 (August 2003) [wn]:
knapsack
n : a bag carried by a strap on your back or shoulder [syn:
backpack, back pack, packsack, rucksack,
haversack]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Knapsack \Knap"sack`\, n. [D. knapzak; knappen to eat + zak a
bag. See Knap, v. t., and Sack.]
A case of canvas, leather, nylon, or other sturdy fabric,
fitted with straps, for carrying on the back the food,
clothing, or other supplies for a soldier or a traveler; as,
to hike up the mountain with lunch in a knapsack.
[1913 Webster +PJC]
And each one fills his knapsack or his scrip
With some rare thing that on the field is found.
--Drayton.
[1913 Webster]