Adv. refines and cave keys. I recommend you buy them now, because there is a possibility that cave key rebate will change (in China you need over 5000 keys for ultimate essence). Bond mysteries can wait, unless you use Jonin Minato.

Buying adv. thread is just not optimal unless your'e finished with rune stones and treasure tools. It is the most overpriced item in the game for the amount of power it brings (maybe on par with purification breakthrough pill). Unless you want to have cool looking battle armor :)