After your jar candles burn out, they can be cleaned out and reused for any number of things – including other candles. One way to clean a candle jar is by setting your oven to 200 degrees, melting the leftover wax, and then pouring it out.
An even better way, though, is to put it in the freezer for an hour and then pry out the frozen block of wax. It should fall right out. If the opening of the jar is smaller, use a butter knife to break the frozen wax in half.