If you have your lead character standing near a teleporter stone you can left click drag and drop it into an open inventory window, or onto a character portrait (though that way you don't get to place it in a specific spot in the inventory). You can use the teleporter stone without dropping it, or click on it in your inventory to teleport to one teleporter stone on the ground somewhere while keeping the one you have with you.
If you summon a doll you can stash any excess loot on it (they can not hold quest items or set/unique items in the act they are found in), and stuff you want to keep on your main characters can be moved to the lower section of the inventory (scroll down), so the stuff that gets added to the top doesn't get cluttered. When you visit a merchant, you just need to summon the doll again and select it if you want to sell / trade anything it has.
