Nomad is a short poem about living on the edge of society, moving through places where nobody really looks at you. The speaker walks "thin," which suggests both hunger and a wish to take up as little space as possible. Being unobserved seems to be a kind of protection, but it also hints at loneliness.
The second stanza is the bleakest. "Bag people" are people who carry their belongings in bags, and their dinner is "ash and air": nothing to eat, only leftovers of burned things and empty breath. The image is stark and almost bitter.
In the last stanza, the speaker speaks to a "brother," asking to be seen as they leave once more. That small request is the emotional center. The speaker is always departing, and wants at least one person to notice. The mood is quiet, hungry, and lonely, with a thread of tenderness running through it.