People like to be a part of something. They seek community. One good way to developing a tribe around your brand is the ability for your brand to be applied to the audience in a tangible way.
Apparel is a way for people to connect with your brand in that way. In the same way a fan of a sports team connects with that team by buying apparel with the team brand, you too can develop a tribe behind your brand.
Taking a look at several brands whose tribe connects with them, they buy into the community through apparel. The tribe behind Patagonia purchase their products because they believe in the brand. Whether it is Realtree or Mossy Oak, people purchase into the brand based on their connection with them.