Once I carried him milk in a bottleCorked sloppily with paper. (19-20)
We might interpret this as a young boy's contribution to the huge effort his grandfather is making. It's his way of being a part of the peat harvesting.
But I've no spade to follow men like them.
In this line, the speaker both puts himself down (a sort of "I'm not as good as those guys" comment) and praises his father and grandfather. It's a strange combination, but it makes sense when you consider the unique situation in which he finds himself.