Ammo
Ammo is bought from traders or salvaged by logistics drone, and is a requirement to use weapons
Bullets
Bullets are used by Gatling Guns, they come in stacks of 300
Railgun Slugs
Railgun Slugs are used by Railguns, they come in stacks of 10
Cannon Shells
Cannon Shells are used by Cannons, they come in stacks that hold 6.