Whether we like it or not, what we buy says something about who we are. Our identity is interwoven with our consumption. If we choose to eat only vegetables that says something about our worldview. Some buy pickup trucks and sport utility vehicles to show that they are big, powerful people. Others buy small hybrid cars because they believe they are saving the environment. If we believe this to be true then we could subscribe to the idea that every purchase we make says something about who we are, from the ice-cream flavor I like to the color t-shirt I prefer. It is not for me to make any presumptions about what these choices mean for a person. Though we can see that evaluating in general the kinds of things that a person chooses to purchase can be very meaningful in identifying who they are.
Brand choice is the largest of these indicators. In my classroom, in a matter of seconds, my students can identify how cool a person is depending on the brands of their clothes. An interesting activity a teacher might do with their students would be to have them itemize the things that they own, and create a kind of profile about what those things say about themselves. This would get students thinking creatively and concretely about these issues. Of course some one who would fall into the social category of nerd does not become cool if he wears the right brand.