Choosing the Number of Items to Split
There needs to be a way to choose the # of items you want split from a stack. You could make the default number of items in the text box half the stack you're splitting so all you have to do is hit "enter" to preserve the old split functionality. There should also be a keyboard shortcut for split commands (something like shift+left click or perhaps shift+drag left click to an empty space).
An inventory sort button would also be nice. It would also be nice if it worked for both your personal inventory and all in-game containers. Here are some suggestions for modes.:
Item type (something like tools+weapons on top, followed by wood, stone, metal ore, plants, then animal materials)
Quantity (Highest number of items on the top, lowest on the bottom. Good for making it easy to decide what parts of your inventory you want to throw out when you're on a long farming trip)
Item Transfer Hotkey
Now, I'm not sure if the devs purposely left out an item transfer shortcut so that it's harder to loot an enemy's body in combat or if it's just low on their list of priorities. It would be helpful to have a shortcut like ctrl+left click to automatically transfer an item to or from whatever container you have open. Would make it easier to fill up your bloomery with ore, loot a dead body, or drop off things into your containers.