In my dictionary, drin is an idiomatic component of both drin sein (to be into it), and das ist doch nicht drin (that's not on).
But I'm not sure which of these meanings go into this newspapers title:
I would translate this idiomatically as
Translating it more or less literally, it means "It's not empty yet" (to be precise: "It contains more.")
Drin (or darin) literally means "inside that" but is also often the translation for just inside. So
and this is used in all kinds of expressions both abstract or literal, two of which you mentioned. The headline just uses the same abstract idea like the second of your examples... think of it this way: you have a bag out of which you take "life". If something is not inside, that means you can't do it. If there is more drin that means you can do more.