Well, really? I find more than enough purpose to go on, to try to be good and do good, just in the here and now. This needs a book, not just a 3-liner, but then there are plenty of books about it already (needless to say I don't mean those of Dawkins and the rest of the atheist-evangelical rabble). Natural life does not feel to me so small or terrible or bleak that I need an afterlife to make it not nonsense.
Stevens wrote a poem to the effect that if (as) life is finite, and there is no afterlife, that makes the life we do have all the more -- infinitely more -- precious for it.
I wish we had more of life span, but that is not quite the same thing. In any event I have enough reverence for the reality principle (most days!) not to project that wish onto the screen we call the hereafter.
Now I have frightened myself and must go dig out my old copy of The Courage to Be.