It popped up to me that it could be a typical Hughesean macabre way of referring to the protagonist's ancestors' cremation remains, put into a sachet bag.
This interpretation suits well to the refraining chorus of burned up objects, and also with those two lines that refer to mourning and burial:
> [...]
> The spark that banged burned out his weeper.
> So he leaned one hand on a gravestone
> [...]