Contains all I/O connectors, just standard 2,54 mm one or two row Pinheader, available in any electronic parts store. price around 1-2 Euro
2×10, 2×11 and 2×13 pins Pinheader, e.g. Reichelt SL 2X10G 2,54 and SL 2X13G 2,54 (Reichelt has no 2×11 pin headers, you can take the 2×13 and cut it off)
If you need (Not in Kit):
JTAG is 2×5 Pinheader, on backside under display (Reichelt MPE 087-2-010)
ISP is 1×6 Pinheader, on backside under display (Reichelt MPE 087-1-006)
X1 is 2×10 SMD Pinheader, on backside under headphone (Reichelt SL 2x10G SMD2,54)