Torchlight has a fantastic game mechanic that it borrows from its ancestor, Fate. Players have a pet that not only serves as a combat companion, but also a handy remote access to shops. Specifically, you can load the critter down with vendor trash, and send it on its way to go sell the junk. It will bring back cash and empty pockets to start the cycle again. You need never leave the dungeon whilst adventuring to take care of the “inventory management” vendor dump timesink minigame.
I want a pet like that in these MMO things that I play. In fact, I think they would be a perfect Item Shop sale. It’s an anti-timesink mechanic, so subscription games won’t likely bother (WoW’s vendor mounts and Jeeves being the obvious exception, though notably only present now that the game is older), but for nonsub games that monetize via convenience and vanity items, it strikes me that these convenience/combat pets would be a hot seller. Games like DDO already sell bigger backpacks, so the philosophy of monetizing the inventory management minigame is there.