I was about to suggest something, and I saw this to be the right place. I agree with items like memory, knowledge etc which cant be splitted, but items like water, branches, lumber etc can be quantified, they are measurable, so I feel it would be better if we could quantify it for example
Water - in litres (say player has 15 water and say 10 Water makes 1 litres and then it should become 1lit Water and 5Water (2 items). Similarly other items. I am just putting a possibility here.
Sand - In kg
Branch - In numbers
Another thing would be to globalize the item trade by setting up a Resource shop (similar to the armor shop), so that the collectors can dump in their collections and people can buy on their own (resources are to be consumed and hence trade is necessary) and the money goes to the treasury of the respective guilds. I know it requires a lot of effort but I would feel it is good and it will help the collectors too.
-rider