First aid kit

The first aid kit, also sometimes known as a med kit or health pack, is used to heal any damage the Survivors might take during a campaign. First aid kits can always be found inside of safe rooms, and also during the finale of a campaign (except if the game is being played on expert difficulty, in which case they will be replaced by pain pills). They can also be found in first aid stations and anywhere else throughout the campaign, though this is very rare.

Usage
It takes 5 seconds to use the first aid kit to heal yourself or another Survivor, during which time you cannot defend yourself in any way. Instead of restoring a set amount of health, first aid kits will only restore 80% of the damage the Survivor has taken. For example, if a Survivor has taken 70% damage, using a first aid kit will add 56% (80% of 70) to the Survivor's health, bringing the Survivor to 86% health. This healing is not based on any temporary health a Survivor might have after taking pain pills, and will remove any extra health gained by them. Please note that one first aid kit can never bring a Survivor back to 100% health, and using more to do so would be wasteful.

If a Survivor has been incapacitated and then revived, they will "bleed", causing their health to drop every second until they have 1% left. Using a first aid kit will stop the bleeding and restore the Survivor to 80% health. In addition, this will also prevent the Survivor from dying if they were to become incapacitated again.

As a weapon
A Survivor can use their melee attack while they are holding the first aid kit, though this should only be used in the most desperate of situations considering the fact that pistols never run out of ammunition.