Container of lubricating oil.
Hydrophobic, flammable, precious oil has seen a wide variety of uses for thousands of years. Oil is used in cooking, cosmetology, fuel, and even paint. Oil is also commonly used as a lubricant, due to its "slippery" properties that greatly reduce friction, which prevents mechanical parts from jamming and reduces wear and tear. Lubricating oil also sees use in firearm maintenance as well; a well oiled firearm is less likely to jam or fail.
Sold in hardware stores and warehouses and included in firearm maintenance kits.