Hikers' burdens refer to the items that hikers carry with them on their journeys. The two most common items are knapsacks and backpacks, both of which have nine letters. Knapsacks are typically smaller and more lightweight than backpacks, and are designed to be carried over one shoulder. Backpacks are larger and heavier, and are designed to be worn on both shoulders. Both items are essential for hikers, as they provide a way to store and transport supplies and equipment.