A metaphor compares two seemingly unlike things to make a point. An extended metaphor is one that examines an initial metaphor in greater depth. A simile is a form of metaphor that uses the words like or as.
The extended metaphor in Hurston's essay comes at the end. Here, she compares skin color to the outside color of a bag. First, she compares her own skin tone to a brown bag, stating,
I feel like a brown bag of miscellany propped against a wall.
She then extends this metaphor to include "other bags, white, red and yellow." She goes even further with this idea. She pictures dumping out the contents of all the different bags. Each one, she says, contains a jumble of items, some of great value, others of no value. She asserts that if the items from each bag are all mixed together in one pile and then randomly replaced in the colored bags, it won't make much difference.
By this, she is explaining that beneath the surface of different skin colors, people are fundamentally the same. We are all a mix of good and bad. No one race has a monopoly on value and no one race is worthless. By using this metaphor, Hurston communicates that all people are equal. She does so in a way that is concrete, visual, and easy for readers to understand, making this one of the strongest parts of her essay.