I didn't use bobbins, because there were so many and they would get horribly tangled. I just had about 1 yard (meter) of each colour and left it hanging like strings - this is much easier to comb out when they get tangled. It looks nicer to do the intarsia, and the over stiching rather than stranding, because it changes the texture on the flap. I did stranding on the edges like the pattern says.
Good luck - the results are well worth it.....I have made two bags now with the same kit......and my sister and I love them.