The following weapon enhancements are designed to augment your firepower, and apply to Primary Weapons and Pistols (but not Melee Weapons). They are carried on your back, only carry one at a time. As First Aid Kits are also Backpack Items, it is usually better to pick up one of these Packs, instantly use it, and then pick up the First Aid Kit you dropped.
Up to four teammates should pick up and add augmented shells/bullets to their Primary Weapons. This is done automatically, and the subsequent shots are of this type. You cannot choose when to employ the shots once the ammo pack has been added to your equipment.
Although one teammate has to sacrifice carrying a First Aid Kit on their back, it is better to keep an Ammo Pack until you really need it, such as during a finale or when you’re about to repel a large number of foes or a Special Infected. However, because First Aid is usually more helpful to an Ammo Pack carrier in the long run, immediate distribution usually occurs.
Explosive Ammo Pack
When taken, your next magazine or rounds are fully-stocked with explosive ammunition (except for the M60; only the remaining ammunition is transformed). They immediately dispatch most Infected with a blast similar to that of a Grenade Launcher, which can knock down other foes in the vicinity, and wound them even if the shot impacts a nearby wall, close to a foe.
It is useful to pepper these explosive rounds into larger Special Infected such as the Tank too, or to cause a Witch to be knocked back, preventing her from reaching you or a teammate. Use them sparingly, and with weapons that have sizable magazines.
Incendiary Ammo Pack
When taken, your next magazine or rounds are fully-stocked with incendiary ammunition (except for the M60; only the remaining ammunition is transformed), meaning they immediately set a target on fire, burning for around five seconds. This helps nullify large numbers of Common Infected, as well as Special Infected, although your vision is reduced through the haze of staggering, burning bodies. Each shot kills a Common and Uncommon Infected, so use them sparingly, and with weapons that have sizable magazines.
Laser Sight
This Laser Sight is found and deployed simultaneously, so it isn’t something you carry around with you. When taken, it adds a red laser sight to your Primary Weapon (and Pistols or Magnum, if you have them instead of Melee Weapons).
The Laser Sight helps you aim, but disappears when you drop a weapon to pick up another, so use this only with a favorite firearm.