Well without doing anything fancy like StonedSoldier's script you could try creating a weapon holder and then adding a weapon to it. A weapon holder is like an invisible ammo crate. Here is the code I used for one of my missions:
_whx = 7146
_why = 6050.5
_whz = 0.1
wH1 = "weaponHolder" createVehicle [_whx,_why,_whz]
wH1 addMagazineCargo ["M16", 2]
wH1 addWeaponCargo ["M16", 1]
wH1 setPos [_whx,_why,_whz]
wH1 setDir 240
wH2 = "weaponHolder" createVehicle [_whx,_why,_whz]
wH2 addMagazineCargo ["HandGrenade", 2]
wH2 setPos [_whx+1.7,_why+1.4,_whz]
wH2 setDir 45
It creates two weapon holders and puts an M16 + 2 mags in one and 2 handgrenades in the other.
Bye the way a weapon holder that just has ammo - or grenades looks like quite a neat satchel, a weapon holder with a weapon in is invisible and you just see the weapon. The weapons should be lying down. You can alter the vertical height by changing whz. I have it set to 0.1 beacuse they are to be placed inside a building. You can put them on top of tables by setting whz = 1 (ish) you need to experiment. To get them to be at different angles you would need StonedSoldier's script - and I don't have it.