Displaying items by categories in the inventory will be cool!
As for sorting, large to small isn't too bad but that's not much to go from. There's a whole lot of 3x2, 3x1 and 1x1 items, Is it done by listOrder currently? That's what I would prefer to see. Then it groups all your melee weapons first, then guns, sort of by damage/tech level, then equipment.
I don't really care for "maximum packing", ie filling all the squares at the beginning. In fact, it tends to make things really hard to find since their positions depend on what else you have packed. Personally, ordering by list order would be best. That keeps clips next to their guns and things sorted in the way we are used to from the items lists.