Thinking about void, nothing, inexistence alone is enough to turn your brain into scrambled eggs... if you take the metaphysical point of view, then "nothing" doesn't exist at all. It's just a word we invented in order to have an opposite concept for "something", for "existence" or whatever you want. We couldn't speak of light if darkness didn't exist as well. We cannot grasp anything in an absolute way, I think. All we can do is compare, contrast, categorise... we see everything in relation to something else. Everything comes in pairs (or in more complex patterns) and only makes sense that way (to us, at least). The funny thing when talking about existence is that in this case the counterpart, which is essential for us to be able to talk about existence, does not exist. o_O
And the purpose of life, phew... the first replies given here aimed at some species or another, but I don't know if you can separate them from the rest. At a first glance, the purpose of the life of a duck may be to keep the duck population at at least the same level, ensuring the species' survival. But what the heck are ducks doing here, anyway? (Not that I bear any grudge against ducks, don't worry...) What's the purpose - not of the life of one or another species, but of life itself?
I think that whatever it may be, we'll probably not be able to conceive it anyway. When we are giving our individual lives a purpose, we do what we always do - we compare and see things in a relative way. We know behaviours we don't want to adopt, we see different ways of living and acting in relation with each other, and we judge and decide Whenever we see something we judge as "good", we have an opposite concept of something "bad" or "evil" in mind. As soon as one of these poles is eliminated, both are unthinkable for us. And what if the purpose of life is something absolute, something that doesn't have an opposite concept? I guess we wouldn't be able to grasp it, it would be beyond our reach.
----------------------
Another approach is this one:
The meaning of life is 42
(Recommended book: Hitchhiker's Guide Through the Galaxy by Douglas Adams (R.I.P.)