Sets Hammer key values on an entity.
Alternatively you can look at the .fgd files shipped with Garry's Mod in the bin/ folder with a text editor to see the key values as they appear in Hammer.
Makes an NPC not drop his weapon and drop a healthkit on death, using SF Enumerations on a Combine Soldier.
A list of spawnflags a Combine Soldier has can be found here.
npc:SetKeyValue( "spawnflags", bit.bor( SF_NPC_NO_WEAPON_DROP, SF_NPC_DROP_HEALTHKIT ) )