What was made out of cash boxes, keys, and padlocks?

There is a heavy supernatural and spiritual element in A Christmas Carol that works against Scrooge's emphasis on hoarding material goods in the present moment, as if there are no consequences after death. While Scrooge thinks the poor should die and relieve England of its excess population, and that all that matters or is real is money, Dickens is at pains to show a larger context.
This larger context starts with the appearance of Marley's ghost. Just the fact of his friend having an afterlife gives Scrooge pause. Then Marley tells him of his suffering. There is divine justice. This is what Marley means when he says that he is wearing a chain forged from cash boxes, keys, and ledgers. Everything material he was so proud of getting and hoarding, rather than sharing with others when he was alive, has become a ball and chain, a heavy burden, that he must drag around in the afterlife.
He comes back to tell his friend Scrooge that he has his priorities all wrong, and that he will be forced to pay in the afterlife, as Marley has, for the selfish, hard-hearted, and money-hungry life he is leading in this life.

To answer this question, take a look at stave one. When the ghost of Jacob Marley appears, the narrator describes that he is wearing chains around his body. These chains are made up of:

Cash-boxes, keys, padlocks, ledgers, deeds, and heavy purses wrought in steel.

Marley goes on to explain that he forged these chains "in life"  and that he must wear them forever. In other words, these items, like the padlock and ledger, are symbolic of greed. When he was alive, he was completely driven by making money. Just like Scrooge, Marley worked in business and his business dealings were chiefly concerned with making himself rich.
By devoting a life to the pursuit of material wealth, Marley pays the ultimate price: when he dies, he must wear these chains forever. Moreover, by visiting Scrooge, he hopes to make him realize that this kind of life is not sustainable: Scrooge must change now or wear the same chains in the afterlife