The Firefly Ice Development Kit has everything you need to get started.  It is all setup for custom firmware development as well as adding an expansion board.

The Firefly Ice development kit includes:

• Firefly Ice printed circuit board assembly.
• 80 mAh Lithium Polymer battery.
• Plastic parts: black top and bottom pieces; plus 1 each of green, pink, blue, and black shell pieces.
• Charging cable.
• Programming cable w/ retaining clip.
• SWD adapter.
• JTAG adapter.
• JTAG USB cable.
• PCBA expansion connector.