How does Frank make the extra money in chapter 17 of Angela's Ashes?

In chapter 17, Frank says that Mrs. Finucane sends him money to take to priests. She hopes that the priests will take the money and in return offer up prayers "for her soul." Mrs. Finucane is convinced that she "is not long for this world" and hopes that by paying for prayers, her soul will be granted an easier passage in the afterlife. Frank, however, decides to keep some of the money for himself, to pay for his trip to America. He says the if he "keep(s) back a few pounds" for himself, nobody, including Mrs. Finucane, will ever know the difference.
When Mrs. Finucane dies, Frank also helps himself to "a roll of money" from her purse. He then takes more money from "the trunk upstairs" and from Mrs. Finucane's ledger, and on his way out he helps himself, for good measure, to a bottle of sherry. Frank uses this money to pay for his fare to America, which he buys for "fifty-five pounds."