The word knapsack can refer to: a backpack Knapsack, Germany, a locality of Hürth, Rhine-Erft district, North Rhine-Westphalia the knapsack problem, a math problem the subset sum problem, a special case of the above Naccache-Stern knapsack cryptosystem, a cryptosystem based on the knapsack problem Knapsack (band), an American band "Knapsack!", an episode of Aqua Teen Hunger Force