In "Great Expectations", what two careers did Mr. Pocket consider when he was younger?

In Chapter 23, Pip visits the Pockets' home with his new friend Herbert. The narrator mentions that when Mr. Pocket was young he was "not quite decided whether to mount to the Woolsack, or to roof himself in with a Mitre."

A footnote in the Norton Critical Edition of the novel explains that the "Woolsack" is the cushion sat upon by the Chairman of the House of Lords, and that the Mitre is the tall, peaked hat worn by the Pope. In other words, Mr. Pocket had his own "great expectations" for his future career.

Source: 

Dickens, Charles. Great Expectations. Ed. Edgar Rosenberg. New York: Norton, 1999.