You have to pull out all that you've already got in storage and then buy more. Or buy ones you've not bought any of yet. But if you're like me you don't want to buy those, if you did you'd have already bought them.
This is why I strongly wish they would simply require you to "HAVE" these items and not "buy". This way if I already have them they get counted and I don't have to buy more of something I don't want.