So unless you're religious, there is no set purpose in life.
What this logically implies is that what one chooses to do with their life cannot be said to be better/worse with what another does with theirs (so long as they are not infringing on the rights of others). For example, living the traditional lifestyle or "american dream" of getting married, having kids, and getting the white picket-fence can't be said to better than the hippie who lives on the road. The "traditional" lifestyle is a societal norm based entirely on human constructs and nothing else. No set, objective criteria exists to compare these two rationally without bias. And so, what is the purpose of living? Is to enjoy the most of it? However "degenerate" that may be? Or is it based on how much we accomplish - how much we contribute to society? Or perhaps it's only based on the relationships we make and the impact we have on other humans?
And perhaps this provides the most significant basis and reason for religion. Religion provides a path; it tells you how you ought to live, which for many, is too compelling of an idea to let go. Knowing how you "ought" to live can make tremendously easier and provide you with the spiritual relief you may need to get through the day.
/rant