If I remember correctly, I think the Third Dawn client let you pop out a list on the side of the backpack view so you could see a list of all the stackable items in the backpack, as well as their quantities. I can't remember if you were also able to do that with other containers. It was nice to be able to see right at a glance how many you had left of each reagent or how much you had of each type of ingot or ore, etc.