Brothers' War Prerelease Kit

 The Borthers' War Prerelease Pack contains 6 Brothers War Draft Boosters, 1 foil-stamped rare or mythic rare card, 1 MTG Arena code card  1 deck box, and 1 Spindown die.

There are 2 boxes Urza's Iron Alliance & Mishra's Burnished Banner. Now, there's no gameplay difference between what you open—no extra themed cards or the like. There are some fun cosmetic ones to keep an eye out for, but don't stress it too much.