Items to Dump for Battle for Azeroth
Bear Tartare and Fighter Chow. Nerfed Dump it.
They will be useful in the first few months of the expansion, but will be replaced by a new bag in BfA crafted by tailors. Keep selling until you run out of stock.
Stockpile [Iceweb Spidersilk] instead. It has been replaced in the materials needed for the tailoring flying carpet mount.
Legion Trade Materials:
Unbroken Claw, Unbroken Tooth, Transmutagens, Empyrium, Felslate, Leystone, all your meat, all your fish, your gems, stonehide leather, stormscale, your herbs, your legion herbalism seeds, Shaldorei Silk and Lightweave, but keep a stack of each for crafting tailoring transmogs.
Hang on to your enchanting mats for now, because enchant scrolls will still sell for the next few months
Except: if you see them being sold at a very very low cost, in which case buy them now for saving for later, as the price may slowly go up again. In 2019 you will be crafting Legion gear for transmog sales. Perhaps keep a few stacks of herbs for inscription.
Don’t dump your Alchemy stock before BfA, because all those potions and flasks will be useable while leveling, both for you and for your customers on the AH.