Slack.
No, not the chat software.
The best company cultures I’ve been part of had 5% more people and time available than work that had to be done. That’s almost unheard of in this day and age, but it makes all the difference in the world.
The stress and pressures and politics of trying to get 10% or 50% or 300% more done than you really have the resources for make people stressed and turn coworker relationships toxic. Everyone’s just struggling to keep their heads above water, and sometimes they have to kick someone else or climb on their back simply in order not to drown.
A little extra time means people have the mental space and the space in their schedules to help one another, to find out what one another are doing (so people and departments can actually coordinate their work) and to get to know one another. People who are under less pressure and less stressed are less likely to snap at one another or resent others’ requests and demands. It makes all the difference in the world.
You know what else helps? Walls.