A package changes your Gun when you touch it. The package is also destroyed.
You know what Gun you are changing to because it is written on the package.
Each time that a package spawns it contains a different random Gun (each Gun has a different chance of appearance).
Packages disappear with time. Creating a sense of urgency and potentially generating situations where you need to take risks to pick a package or leave one that you want just to play it safe.
Ghosts can drop packages when killed.
Packages can be of two types: an ammo or a health pack. You can not get health or ammo back without changing your Gun. Forcing you to adapt to a new one every time you want to heal or reload.
Restores all your ammo.
They disappear quickly.
If you shoot your last bullet and there are no Ammo Packages for you to pick up in the level, an Ammo Package will automatically spawn in the position where you were a couple of seconds ago to make sure you always have enough ammo to keep playing the game. Running out of ammo is still an undesirable scenario, as it will get you unarmed and running around, looking for a package; only able to try to avoid Ghosts until you get a new Gun.
Restores 1 health point.
They last longer than the ammo packages. Because there is no system in place to make 100% sure that you get a health pack, and health being the resource that determines when the game is over, making them last longer will give the players more chances to pick them.