It's vital for Crusoe's survival that he preserve his supplies of gunpowder. For one thing, he'll need it to load his gun when he goes hunting—for without being able to hunt on this remote desert island, he's sure that he'll starve to death. Also, Crusoe will need to have gunpowder in order to ward off any natives that might be in the vicinity. If there are such people on the island, chances are they won't be very glad to see a stranger like Crusoe in their midst.

Despite the gunpowder's importance, however, Crusoe is a little slipshod in protecting it. It's only after he's secured his other provisions inside a tent that he realizes what he's forgotten to do. A sudden thunderstorm, complete with a flash of lightening, brings home to Crusoe how easily his stock of gunpowder can be ruined by the elements. Either it can be damaged by the rain or explode if struck by lightening.

So to protect his stock of gunpowder Crusoe comes up with the idea of dividing it up into little bags and boxes. This way, if the weather should turn nasty, Crusoe will lose, at worst, only some of the gunpowder and not all of it.