There are now rewards in Fortnite: Battle Royale! These include incentives for leveling your Battle Royale account over the course of a Season, and spending your Battle Stars to unlock tiers in the Battle Pass. For more information about the Battle Pass, see here.
Any V-bucks earned by unlocking tiers in the Battle Pass, as well as any Banners unlocked in Battle Royale, can be used in either Save the World or Battle Royale modes.
All other rewards are limited for use only in the Battle Royale mode of Fortnite.