With every bi-weekly update, there are new files added to the game, including skins (outfits), back blings, pickaxes (harvesting tools), gliders, emotes, which should be released in the Fortnite Item Shop in the next couple of weeks. Here are the pickaxes, gliders and back blings that have been found in the v5.4 update, thanks to @TwoEpicBuddies:
These cosmetics should be available in the Fortnite Item Shop some time in the future and can be purchased with the Fortnite currency, V-Bucks. The price of the cosmetics will vary, depending on the rarity of each, with uncommon being the least expensive and legendary being the most. The back blings cannot be purchased separately in the Shop, but will be available with their respective skins. We will be releasing the names and rarities of each of these cosmetics as soon as they are available.
You can see the leaked skins found in the v5.4 files below: