Of course after the wolf update in 1.4 everyone wants mounts and more tameable animals, most are very impractical and just bad ideas. But due to having more and more materials such as food for damn wolves needed, a pack animal would be a great addition. The animal would simply have an inventory the size of the player. The animal would either be slow and have a limit of a few, or be fast and follow the player precisely, and have a limit of one. An animal such as a horse(NOT A MOUNT!!!), a camel(ONCE AGAIN NOT A MOUNT!!!), and a donkey/burrow.
I can't rage at you for any particular reason now, mostly because I just google searched this and it only came up with fully controllable pigs.
Please. Set up your ideas a little, and at least WAIT for your first idea to get a little criticism before posting another idea.