User blog comment:Redkite525/Redkite525's Call of Duty: Modern Warfare 3 Tournament! - Entrance/@comment-5465602-20121001205246/@comment-5790624-20121018203046

' Their weapons - A primary weapon (Assault Rifle/Submachine Gun/Lightmachine Gun), a secondary weapon (Sniper rifle/Shotgun, PDW), Special (Explosive launcher or side arm [G18, etc] with an attachment), Equipment (Claymore, C4, Handgrenade, Flashbang Grenade) and an attachment to go on your pimary or secondary weapon.' 

The 9 bang grenade is an equipment item and you already have C4. The special slot which the Crossbow covers need to be a explosive launcher or a sidearm.