The concept is pretty simple and was asked for some time ago. Still, it`s neat, so why not?
So, one stone(nearly 100g) takes as much place as a pie(1 kg) or moth(less than 5g). Small things which should be hauled in mass are being hauled around like they`re made out of glass. And we`re able to haul hundreds of kg of goods, which is pretty unrealistic aswell.
The idea is: let the weight of the items hauled will determine the capacity of inventory instead of quantity of tile taken.
This way player gets a 8x8 inventory and basic hauling ability of 15 kg. With backpack it`s increased to 25, and with traveller`s sack it`s increased by 3(7 for hi-ql ones, up to 15 for two hi-ql). One can`t lift things if more than half of current weight capacity is used. One can also increase his hauling ability by raising str and con(additional weight hauled = (str+con)/50).
Merchant`s robe, instead of allowing you to haul more, adds a four-slot inventory, into which a flask, keyring, sling or something else which`s not tool but still is something you`d keep with yourself can be added - pockets, in other words.