What do Atheists do?

Are you familiar with meetup.com?
Some meetup groups are religious, some are new agey, some are for fun, some are for exercise. There are all sorts.
My questions is what do atheist groups do?
I can understand pagan groups getting together, meeting in a forest, and worshipping a tree. I really don't know what pagan groups do, but that's what I imagine they do.
Maybe Christian groups sing worship songs or gather for Bible study.
And artistic groups could paint together or do a group trip to a special exhibit.
Tennis lovers get together and play tennis. That makes sense.
What what do atheists do when they hang together?
Talk about what they don't believe. That's a lot of energy to spend for something they don't believe.
They don't worship together because they don't believe in God or the magical powers of a tree, or am I missing something?
How does nothing bind you together?
Do you rage against Christmas and that you get the day off, sometimes with pay?
Are you planning festivus? If so, what are you celebrating?
If you're part of an atheist group, please let me know what you do when you meet up.