The Proton Pack backpack is an Rare Fortnite backpack. Proton Pack was available via the Item Shop for 400 V-Bucks and you can buy it from Fortnite Item Shop when it will listed.
Fortnite Proton Pack Backpack Details
Don't cross the streams.
Fortnite Proton Pack Backpack PNG Images
Here is the PNG images of Proton Pack below!