A weapon can be outfitted with one optics module and at least one other weapons attachment. You can further customize your weapon with different kinds of ammunition depending on weapon type. The charts below present the various attachments and optics in the order in which they can be obtained for their category.
Purchased attachments and optics are weapon specific. You must purchase each attachment or optic individually for every weapon; buying it once does not unlock it for every weapon of that type, only for that specific weapon. If a weapon is shared by 2 classes (Ex: Carbines are shared by Engineers and Light Assaults), or all of them (minus MAX, Ex: Pistol), then attachments purchased for the first class are also unlocked for the other classes.