The Maxim DS3231M is a high precision Real-time-clock with built-in temperature compensated crystal. The I²C interface allows access not only to the date/time, but also to the temperature sensor data.
The small SOIC-8 package is the perfect size for the Whisper Node. The Kit also comes with the required capacitors and resistors in 0603 SMD size.
The upgrade Kits are supplied with all required components. You just need some experience to solder the SMD parts to add some extra features to you Whisper Node. Check the board documentation for all details.