The 28-year-old Selkirk was put ashore with a few basic pieces of gear - a change of clothes and 2 blankets, an iron pan and drinking jar, a bag of tobacco and a Bible. He also had a few weapons including an axe, knife, cutlass, pistol and musket, with a pound of gunpowder.
From "The remarkable adventures of Alexander Selkirk" 1800.
These items, along with his wits and skill, would be enough to see him through his lonely adventure. The many tasks he would have to perform to ensure his survival probably kept him sane during the long isolation.
Selkirk with his goats. (The other animals pictured are just fantasy!)
Early on during his stay, Selkirk noticed the descendants of Juan Fernandez's goats roaming the hills and cliffs of the island. They would provide the castaway with ample food clothing and shelter during his time of the island, as well as proving to be a passable substitute for human companionship.