The third and final "Ranger Survival Guide" trailer for Metro: Last Light is all about the tools would-be adventurers possess for survival and combat.
Two of the most precious resources available to prospective rangers are air and light. The air on the surface and in the transition zones is still toxic as a result of nuclear war, so venturing forth without a gas mask is fatal. Even then, filters only last a limited amount of time before they must be replaced. A lack of light in the metro tunnels is less immediately lethal, but it is still a crucial resource that must be expended with care. The ranger's watch also serves as an indicator of whether a player is concealed in shadow or in enough light to be exposed, so players will need to keep an eye on it.
Intact pre-war weapons are a rarity in the metro, so most guns are hodgepodge jury-rigged Frankenstein creations. Their makeshift nature does not make them any less lethal, though ammunition must be conserved if possible. In lieu of actual money, bullets are used as currency in the metro, and every shot expended on a mutant or bandit is one you won't be able to use to purchase a new gun.
Metro: Last Light will release on Windows PC, Xbox 360 and PlayStation 3 on May 14.