First of all the weapons need to be realistic. No magic involved. No far-fetched stuff. For an example a weapon made out of pure diamond. No weapons that fire off lightning bolts. I hope you get the picture.
You must have a concealable weapon… which means no swords, axes, scythes, hammers, bows and other large weapons. The only exception is if you can realistically conceal these weapons.
You may use weapons like an elbow blade, tonfa, or tonfa-like weapons if you ask an admin for permission first. If you have a weapon in mind that is slightly concealable you need to ask an admin for permission to use it. (Usually acceptable)
Examples of weapons that you can use. Whips Numchucks Guns Collapse-able spear/pole Daggers Knifes
There are more than I can list but I will give a few sites if found with several concealed weapons.