1. rucksack-a bag carried by a strap on your back or shoulder. back pack, backpack, haversack, knapsack, packsack. bag-a flexible container with a single opening; he stuffed his laundry into a large bag. kit bag, kitbag-a knapsack (usually for a soldier).ucksack. n. 1. a large bag, usually having two straps and a supporting frame, carried on the back and often used by climbers, campers, etc. US and Canadian name: backpack. [C19: from German, literally: back sack].