Grenades don't work because flak does not work in arena games. If you try to throw a grenade or shoot a rocket, your game will crash. Dynamic entities in general (excluding weapons, and etc)
DO NOT work in multiplayer either. So the weapons chest will not work. No current mod addresses these problems to my knowledge, though FPSC IP allows you to have a lobby system, as well as up to 1,000 maps to chose from in a single game.
Yes, you can use DB Pro to create your own mod (it comes with the source to FPS Creator), and take a shot at adding these features yourself, but other than that, you're limited to picking up weapons and ammo, and shooting other players.
Kravenwolf