I just started working in a small lab a few months ago. I don't know if the way our lab is functioning is right or even good, but I like it, it works for me and I feel good here, so let me explain the lab dynamic here.
Just to give some context, the lab is so small that the division to project teams (although it exists) does not make sense for any informal activity. At any given time, there is 7 - 10 PhD students in the lab, maybe 1 or 2 exchange students/interns, and we have some PhD students that are in the lab only a day or two a week. Also, the lab is almost circular, all the offices are very close and we have a habit working with open office doors.
The common topic denominator among all of us is "Computer Science" (very broad), although each of us can find one or two more student-people working a similar topic.
I find that it's much easier for me to talk science to somebody I feel comfortable having a beer and a few laughs with as well. Not saying that you have to get your lab drunk, but:
in the morning, the first one in makes the coffee, and we linger in the lab-kitchen for 20-30 minutes until our eyes are open. Everybody is free to join, heavy coffee drinkers are almost always there, while the others wander in from time to time. Sometimes even the senior researchers have coffee with us.
we all go to lunch together (partially cause we all have partially refunded meals in that resto). We have a guy who talks much and eats slow, so by the time everybody finishes, we usually spend a quality 30-40 minutes talking. We also do a coffee after lunch.
When somebody's leaving the lab, we try to buy some trinkets (last time it was 1euro/person), organize small going away "party" in the lab with juice and cookies, and dinner followed by drinks in the evening. Food setting is more inviting to the shy students, and after that the outgoing ones go have a few pints.
Students sometimes just wander in other student's offices (usually in the lazy afternoon hours) for a few words. This habit is nice because you feel less uneasy when you stroll into somebodies office to talk science, cause you're practically doing the same thing. As a less imposing version, we sometimes just wave to each other while passing in front of the office.
When we have organized (boring) activities / administrative seminars / things that finish early, especially out of the lab, we try to go sit for drinks if we have time.
the only nice idea specifically targeted for professional exchange we did was organize a "PhD students day" where we all presented our subjects in very basic streaks, from 10 - 15 minutes, so that everybody would know which students are working on interesting problems (for them).
every project team has team meetings at their own pace, where we present our current research, recently accepted papers, exchange students present their topics or students that went to an exchange present what they did. My team does it usually two times a month, in a fairly casual setting.
Now that I mentioned all this procrastinating, let me say something that's always been true for me among Computer Science people wherever I went (studied in Croatia, Austria and now France, and had some holidays with CS people): you can't stop computer scientists talking about tech. Tech talk bleeds through beer, we eat some of it for lunch and drink it in our coffee. When we're happy about our work, we feel comfortable enough to share it with people around us. When we're angry and stuck, we are all around people who saw us in various kinds of settings, so we don't feel that uncomfortable being grumpy and complaining.
All this said, for some more context: I'm a PhD student in France. I have a feeling that the work environment here is much much more relaxed that in the States, and than a lot of European countries as well. They seem to believe that if you do everything slowly and relaxed (except a day before a deadline), you will do a good job. So, my advice might be only applicable to similar work cultures, but I still think there's some good things there, because, at the end of the day, we all enjoy our times in the lab.