From Longman Dictionary of Contemporary Englishbackpackback‧pack /ˈbækpæk/ ●●○ noun [countable] 
DLOa rucksack
DLOa rucksackExamples from the Corpus
backpack• Ellis stood near the appointed place, carrying a backpack he had bought in a cheap luggage store.• He reached into a backpack and pulled out a small rug and put it out in front of me.• At every turn new ecologies open at our feet, and I fill my pockets and backpack with interesting new specimens.• Her backpack must have weighed twenty pounds.• He is 24, moustachioed and wearing a small backpack.• The M-16, the. 45 Colt, the ammunition, the backpack of water canisters and chow.• If the backpack gets too heavy, of course, you could always canoe back down the river to Chepstow!• It was noisy and crowded, the concourses and passages full of tourists, hundreds of schoolchildren and students with backpacks. 