Blended banana buddy.
Smoothie backpack is a Rare Fortnite Backpack from the Bunker Days set. Back bling Smoothie is reactive. It means it changes or evolves (reacts) depending on certain things in game (damage dealt to opponents, if it's day or night...)
The Set Bunker Days contains 8 cosmetic items.
The backbling Smoothie belongs to Chapter 1 Season 9. It's not yet known how to get the backbling Smoothie.