When people play outdoors - when they hike, camp, raft, or climb - they want to carry as little extra weight as possible. And anything they carry has to have a place, which could mean even more weight. The designers of the Rocky S2V, a durable hiking boot, found a place within each boot to store fire-starting material. That means a little less space needed in a backpack, which means a little less material and a little less weight.
This small innovation might not make much of a difference for users (and rather than filling an empty space, the firestarter is probably in a place where there would be cushioning), but what if this kind of thinking was applied elsewhere? What empty space is hiding in our cars, buildings, furniture, or other products? Could it be eliminated, reducing the amount of materials used in the first place? If not, how could it be put to use?