Every week someone in CAM hosts a 1+ hour event that serves as a communal break period for CAM. First-years are not required to host one this semester, but are highly recommended to host in the Spring. That goes double for old-timers.
Anything you want! Often people bring snacks and other extravagant things, but something as simple as bringing coffee is appreciated! You can also host a more active coffee hour (e.g. origami hour).
Steve Strogatz generously started a CAM social fund, which can be used for coffee hour reimbursements. See Erika for details.