I agree with saddlesores, cable housings seem extreme to me. Is there a reason you feel you will need them? I'd probably drop tubes to two spares and a patch kit, too. Not sure how roads are over there that you are worried about damage, but if I can get tires overnighted to anywhere, I'd probably only want one spare.

I'd personally strap the backpack to the rack, and put the guitar on your back too