Etymology From Low German knapzak or Dutch knapzak (older form cnapsack), from Middle Dutch cnappen (“to bite with teeth”), ultimately from knappen (“to eat, crack”), of imitative origin, + sack. German Knappsack is from Dutch.
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US, Archaic, In UK A case of canvas or leather, for carrying items on the back.
1936, Arthur Ransome, Pigeon Post, ch 3. "All but Nancy carried knapsacks, with sandwiches and thermos flasks of tea. Peggy’s knapsack held Nancy’s provisions as well as her own, for on Nancy’s shoulders, instead of a knapsack, was a pigeon-basket […]"
The two elder reluctantly left him and walked on, taking their brother's knapsack to relieve him in following, and the youngest entered the field.1891, Thomas Hardy, Tess of the d'Urbervilles, volume 1, London: James R. Osgood, McIlvaine and Co., page 23:
Etymology From Low German knapzak or Dutch knapzak (older form cnapsack), from Middle Dutch cnappen (“to bite with teeth”), ultimately from knappen (“to eat, crack”), of imitative origin, + sack. German Knappsack is from Dutch.
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To go hiking while burdened with a knapsack, usually overnight or for longer.
My sleeping bag fell off my backpack into the water, while we were knapsacking up the mountain.