We have warehouses in different parts of the country where each one has a different amount of inventory of an item. If one of the items you ordered is out of stock in the warehouse nearest to you, it may shipped from another. This may cause one of the items to arrive sooner than the other.
Rest assured your other item will reach home soon enough. If you want to track it down, visit our Track Your Order page by clicking this link.
If you need more info on the order status, you can find answers in this article.