First Aid Kit is one of the 6 quest items the player has to collect in the Hatchwood Wilds for Lucas Hardy during the sidequest "Hookbilled!" (LH0001).
The First Aid Kits are also a series of 8 quest items that the player can find inside 10 crates located in Paydirt Summit during the sidequest "Medical Supplies" (SV0001) assigned by Skylark Vesper; those quest items will be delivered to all the Banderos in Ridgeback Highlands.