Why this love to limited slots and unability to segregate, with wondering where is some free slot, to drop there and item? I fail to see what's advantage of such a system, besides ability to put different items into patterns you like.
There are many categories for items, like raw materials, aimal parts, ides, armor, food and so on. Items should be segregated with such categories under different tabs and then limited amount of slots seems pointless too.
Maybe i manage to draw it later, for the sake of arty stuff \o/ \o/