Just anecdotally, but every team I've been on where we ate lunch together was amazing, and every team where we didn't was joyless. Eating together of course doesn't cause amazing teams (but it can help), but seems to happen naturally when the team gels. I also like to invite random people from outside our team to come eat with the group, just grabbing someone in the hallway as we head out ("hey we're going to X, want to join?"), it's great for building connections in the org.