Ah, a very real packing problem. [0] The difficulty really skyrockets when it gets recursively complex for orders full of knapsacks [1] But the really dangerous orders come at the beginning of each school year, when students flock to amazon and purchases both knapsacks and textbooks about the knapsack problem.
[0] https://en.wikipedia.org/wiki/Packing_problems
[1] https://en.wikipedia.org/wiki/Knapsack_problem