One of the coolest changes in Patch 3.0.2 is the way mounts and vanity pets work. Done as a way to save bag space, this is great news for collectors and might even spur other players to start collecting, too. On live servers, pets and mounts summoned through the use of an item. When tomorrow's patch goes live, these pets and mounts will become consumable, single-charge items that teach you a spell to summon the relevant pet or mount.
The pet or mount will then disappear from your inventory. Don't panic, those simply become spells that you will be able to access through your Character panel. There's a tab there labeled 'Pets', which will contain two sub-tabs called 'Companions' and 'Mounts'. Selected pets and mounts will be previewed in the window, and you can easily drag your pet and mount spells to your hotbars. Pets are instant cast spells that can be cast while moving and activate the GCD. You can create macros and key bindings for pets and mounts just as you would any other spell.