Smell
The sense of smell is a particularly unusual sense, in that it is so poorly understood by science but still has such incredible strength in drawing things back into the human memory. Smell is also a vital sense for many animals, who rely on it for finding mates, identifying children, finding prey, avoiding predators, and a world of other functions. Humans' poorly trained noses miss an entire world of stimuli of which our dogs and cats are intimately aware.
To help campers explore their sense of smell, you can use a matching activity similar to the one in which campers pair up by the noises that they make, but replace noises with various smells. Alternately, explore leaves and plants that have distinct smells in camp and use these as examples for your campers. Note that the human sense of smell is very weak compared with other animals, and so there is a whole world of stimuli of which humans are not aware.