You have to examine every single item in the game. Here's a list.
Handgun (9mm pistol)
Dmp (UZI machine pistol)
Fixed Butterfly (revolver)
Killer6 (Desert Eagle)
Shotgun (shotgun with wooden finish)
Riotgun (shotgun with black and stainless steel finish)
Dlaser-93s (bolt-action sniper with wooden finish)
Nk-13 (semi-auto sniper with camo print)
Rocket Launcher
Red Smoke Grenade
Green Smoke Grenade
Yellow Smoke Grenade
Hg Ammo (handgun ammo)
Mp Ammo (machine pistol ammo)
Mg Ammo (magnum ammo)
Sg Ammo (shotgun ammo)
Rf Ammo (rifle ammo)
Red Gun Powder
Green Gun Powder
Blue Gun Powder
Brown Egg
Sardine
First Aid Spray
Green Egg
Sardine (rotten)
Green Herb
Red Herb
Yellow Herb
Herbs Vial (G + G)
Herbs Vial (G + G + G)
Herbs Vial (G + R)
Herbs Vial (G + Y)
Herbs Vial (G + R + Y)
Herbs Vial (R + Y)
[Taken from "Define Brackish Water" on Steam]