Apparently if you buy a box of Kaladesh, you can receive a special Buy-a-Box booster pack.

These boosters will contain:

• A premium card from a currently legal Standard set*, including Zendikar Expeditions and Kaladesh Inventions.
• Two non-premium cards that are either rare or a mythic rare from a set currently legal in Standard* (Battle for Zendikar through Kaladesh).

Source: http://magic.wizards.com/en/articles/archive/feature/magic-holiday-gift-guide-and-holiday-buy-box-promotion-2016-11-21