In case you forgot, the Alliance will receive a sword and shield item, while the Horde players will receive the staff of Gul’dan and a battle axe. Note that these items are purely for transmog purposes and have pretty much no useful stats, but if you do like the look and wouldn’t mind be seen wielding them, you can transmog them anytime you want.
Note that these items can be traded across factions. This means that if you have an Alliance character or a Horde character, you can send your goodies to each other, although they will automatically convert to the responding item, so the axe will become the sword and vice versa, but at least players will have the freedom.
Blizzard also notes, “Once the updated Transmogrification system releases with Legion, items received during the promotional period will be automatically added to the Wardrobe even if they have been deleted from your inventory.” This promotion will run until the 1st of August, so if you haven’t logged in already to claim your gifts, you should do so now.