One way to do this is to make a shortcut to the game on your desktop and right click the shortcut and edit the properties. Start the game with the -DEVMODE command line parameter.
There are a lot of parameters to change the weapons, just edit the lua files. You are able to change the amount of ammunition per clip. While in the scripts folder find folders Entities\Weapons. Now you can edit the file to get some advantages: Once opened locate folder Scripts\Default and find the file a Locate your Far Cry\FCData folder and look for the file Scripts.pak Please don't use them while normal gameplay, because the balance will be completely ruined. If you want to have some fun after finishing the game you may try cheat codes.