Tl:dr;
1) Suggestion to add lootsacks as equippable item
2) useless loot can be dropped into the lootsack but will be automatically converted into gold, gold that can ONLY be redeemed at trading posts
3) The lootsack can have unique stats that will add a layer of risk vs rewarddynamic while at the same time make use of the useless loot and add financial incentives for players

I've played tons of Torchlight 2 before, and allowing pets to travel back to town and sell inventory is an excellent way of making a use out of those useless dropped loot

What I'm suggesting is adding a slot in players equipped inventory, where a lootsack can be equipped.

The main function of this lootsack is, players can drop any useless loot that they picked up into the lootsack. The catch is, all items dropped into the lootsack will convert into gold and non-reversible, AND the gold isn't gonna be in the players account, what I'm saying is the value of the lootsack itself will increase the more items dropped into it, but the players can only redeem gold in trading, that means it resets once an expedition failed or a player dies or something.

The reason why I suggest that the lootsack should be an item that can be equipped so that the lootsack themselves can have stats, such as the normal ones either "+10 ferocity etc" or the unique ones such as "Enemies grew stronger as more gold stored in this lootsack", or "the beholder of this sack will be permanently cursed/bleed once the value reaches certain threshold until it is redeemed" or dropping certain gems into the lootsack will alter it's gold multiplication values so on and so forth.

This will add a new risk vs reward gameplay dynamic while at the same time making use of those useless loots that I have to trade with another useless loot all the time AND allowing players to have some financial incentives, A WIN-WIN-WIN.