Many Christians will argue that without God there is no meaning nor purpose to life. I think this is mostly a scare tactic for other believers, rather than it being even an attempt to convince non-believers. (It's a scare-tactic in the form of "if you ever stop believing, your life will stop having any meaning and purpose, you will become just an empty shell of your former self, and you will probably fall into depression, crime, drugs or worse, so don't even consider it!")
No skeptic/atheist has any problem in finding meaning and purpose to their and other people's lives (perhaps those with clinical depression notwithstanding, but that's a completely different reason.) Let me posit this reasoning in a slightly more philosophical manner than usual.
Ideas can be a very strong and influential phenomenon. Ideas can be "contagious", they can "live on" so to speak, by transferring from one person to another. Ideas can change lives, for better or for worse. Ideas can improve people's lives, advance our culture and understanding, drive progress. On the other side of the coin, ideas can delude people, drive them to believe and do foolish things, to behave in all kinds of irrational ways that can be even harmful both to themselves and those around them. Some of these ideas can be extremely persistent and effectively "refuse to die", no matter how hard killing them is attempted. These are often alluded to as "viruses of the mind." Many people say that, for example, religions are such viruses of the mind.
Comparing these strong and widespread ideas to viruses is quite fitting. Like viruses, also these ideas change over time and fight for survival. The strongest, most "contagious" ideas will override the weaker ones. Any changes to these ideas that make them even stronger are retained, while changes that make them weaker tend to be dropped off. This is natural selection in action, on the level of ideas.
People can produce and have effect on these ideas, both the good and the bad ones. A person's actions can affect other people, and the repercussions of these actions can last for much longer than that person's lifetime.
It is thus not at all inconsequential what we do with our lives. Our actions and our ideas can help people, or they can hurt people, and the effects can potentially last for surprisingly long times.
Thus we can clearly see that even a full-fledged atheist can have a clear and important goal and purpose to his or her life: To make the world a better place through their actions and ideas. To have their ideas matter.
It is often said that the deceased live on in the memories of their friends and relatives. This is more than just a poetic idea. This can be a real, concrete effect that truly affects people's lives, sometimes for very long time after death.