Indoors, run the smells in the air demonstration, to show that a smell is molecules floating through the air that reach our nose. (It will not work well outdoors with a breeze that blows molecules away.)
Do a selection of the other activities that relate to smells:
Visual deprivation walk to use our sense of smell when sight is lost.
Taste candy/ice cream with no sense of smell, to find out how taste relies a lot on smell.
Visit a garden or store to smell (and identify) herbs and flowers.
Make perfume with herbs/fruit peels/flowers.
Cook an aromatic snack e.g. oat bars, and compare the ingredients' smell before and after cooking.
Gordon Elementary science club did Smells in the Air Demo, Oat seed bars, Perfume making.
isas Spring 2017 did Smells in the Air demo, visual deprivation walk with visit to a plant store to smell and ID herbs, Tasting without smell at an ice cream store, Perfume making.