Grenade Launcher

In the pilot episode a grenade launcher is seen in the weapons box in the trunk of the Impala. It is occasionally seen there in future episodes, but never used by the Winchesters. This became something of a running joke in fandom, given there were many circumstances when it would have been useful. In the pilot, the weapon seen is a CAW 40mm Grenade Launcher airsoft grenade launcher. In later episodes this is substituted with a genuine DefTech 37mm launcher.

In 12.05 The One You've Been Waiting For, as Dean and Sam head to face the Thule Society, Dean remarks that he "should've bought the grenade launcher," as Sam had told to leave it in the trunk, as they needed to be stealth.

Grenade launcher (bottom right) in 1.01 Pilot.

Dean picks up the grenade launcher in a promo still from 11.01 Out of the Darkness, Into the Fire.

Dean holding the grenade launcher in 12.05 The One You've Been Waiting For.