The act of digging (allegory)
To the speaker, the digging his father and grandfather did proved their worth; he brags that his grandfather dug better than anyone else working on the same bog, and this is a point of pride for him. He compares what his grandfather and father did to his career as a writer; he says his pen is like his shovel.
The pen (symbol)
The speaker's pen is the subject of an interesting transition in the poem. The first lines of the poem describe it and compare how it fits in the speaker's hand to how a gun would. The way it fits strikes a parallel, however, with the description of the shovel fitted with his father's legs and boots. This group of images is used to develop the speaker's idea of work and what symbols he associates with it.
Potatoes (symbol)
Potatoes in 20th century Ireland were an important dietary staple, and they are central to the speaker's family's way of life. The speaker describes them in a manner that makes them very tangible; they root the speaker in his past. However, this is undercut by the memories of the Great Potato Famine, which the poet does not mention but that nevertheless serves as the implicit backdrop to this poem.
Milk (symbol)
The milk that the speaker remembers bringing to his grandfather symbolizes sustenance and reflects the rural way the speaker grew up; by having the bottle corked "sloppily with paper," the speaker tells the reader that this milk likely came from their farm, not from a shop.
