Bite the silver band around the overused eraser once. The top of the eraser will squeeze out of the pencil, giving you at least 5 more turns.
If it is a super cheap pencil, you should be able to peel the flimsy silver band from it if it flattens out again. Be careful though, with no support it may come off in one stroke.
Also if you are careful and of age, sharpen your pencil with a knife, like you would an arrow. You can sharpen your pencil all the way down to a knub and when it gets too small to grasp, tie it to your finger with a rubber band. People will think you are writing with your fingernail!
My kid once used one pencil for an entire semester.
