Some kind of transportation item - a phylactery bauble or bone sack, maybe, into which you can stuff skeletons so as to move them between dimensions or sneak them into diplomatic negotiations. This is really the thing I want most. Minecraft just isn't good at pathing, and being able to carry your creatures around is a huge headache relief, especially when other mods get involved and you're going on long swims or airborne or even just spider-crawling up walls.