According to Wikipedia “Robinson Crusoe is an English adventure novel by Daniel Defoe, first published on 25 April 1719. Written with a combination of Epistolary, confessional, and didactic forms, the book follows the title character after he is cast away and spends 28 years on a remote tropical desert island near the coasts of Venezuela and Trinidad, encountering cannibals, captives, and mutineers before being rescued.” According to Wikipedia, “Daniel Defoe was an English writer, trader, journalist, pamphleteer and spy. He is most famous for his novel Robinson Crusoe, published in 1719, which is claimed to be second only to the Bible in its number of translations.” Robinson Crusoe is still widely read today. 

Why did Robinson Crusoe take the coins off the ship? Here is a recap of what I have read so far. First Robinson Crusoe leaves his home on a boat in search of an adventure, but he comes upon a storm. After this storm is over the boat is still floating. A couple days later another storm hits the ship and the ship sinks. Robinson Crusoe and a few other men escape in lifeboats. Later in the book Robinson Crusoe is enslaved in England for a few years. When he gets a chance to escape on a small boat with another slave, he does. After a couple weeks they come across a Portuguese ship. The man in charge buys Robinson Crusoe’s boat and takes them to South America. Robinson Crusoe builds a plantation there and becomes wealthy, but he wants more money. His friend asks him to take a ship to Africa and get some slaves. He tells Robinson Crusoe he’ll get paid so Robinson Crusoe accepts. On the way there a storm hits and Robinson Crusoe with the other men jump off the ship thinking that it will sink. Robinson Crusoe swims to an Island and when the storm is over the ship is still there, but all of the other people drowned. Robinson Crusoe swims to the ship and builds a raft so he can bring helpful things back to the island to help him survive. For the next few days he brings things from the ship to the island. This includes a dog and some cats. One night there is a storm and the ship sinks. A few months later the ship reappears and is much closer to shore. Robinson Crusoe goes to take more things off the ship and he finds a bag of coins. He decides to leave them because they would be useless on the island, but then he changes his mind and takes them. 

There are many reasons why Robinson Crusoe took the coins, but I think the most common reason is that he could use them to barter himself off the island if another ship came.