What is the meaning of 'knap' as in knapsack? The dictionary doesn't answer it for me.

Etymology: Low German knappsack or Dutch knapzak, from Low German and Dutch knappen to make a snapping noise, eat + Low German sack or Dutch zak sack Date: 1603 : a bag (as of canvas or nylon) strapped on the back and used for carrying supplies or personal belongings.

- From MERRIAM-WEBSTER Dictionary

Additionally: A knapsack is where a soldier carried his food, which might have to be eaten quickly. "Knapsack" meant "eating bag" in the English spoken in the 1600s. Knap comes from a German word that means "a bite" or "snap."

http://www.wordsmyth.net/live/home.php?script=wcd&match=22822&matchsenses=2282201

1603, from Low Ger. Knapsack (Du. knapzak), probably from knappen "to eat" lit. "to crack, snap" + Sack "bag."

http://www.etymonline.com/index.php?search=knapsack&searchmode=none