The prepared versus the unprepared traveller

On a near-month's trip through Java in early 2018 I was taken aback by the size of my travel companion Sally’s backpack and daypack. Hers were almost splitting at the seams; my pack and daypack were each less than half full. At a train station weigh in, Sally’s gear totalled 24 kilograms while mine came in at nine. Why? It turned out Sally was a prepared traveller, while I was far from this.