A ganger hanging about with a gun in one hand and munching on a taco with the other, once in combat, will try and attack with both the gun and the taco. Currently the solution to this seems to be dropping the taco or sticking in in you pocket or similar.
I personally think that someone using a one handed weapon should be able to hold something in their offhand while fighting exclusively with their chosen weapon. This is what the old dual wielding system was all about. Holding two weapons and switching between them.
To bring back a little of this flexibility I think it would be nice to add a 'focus' command. This way you can tell the game that, if possible, you want to only attack with the specified held weapon.
Now if the taco munching, gun wielding ganger is in combat, they can just 'focus gun' and will just shoot at the enemy instead of trying to stab them with a taco. Of course, for those who WANT to stab them with a taco they can continue dual wielding as is the default or to 'focus taco' if they want to really make a statement.
As I envision this, it would be similar to the old 'switchto' command in that it can only be used in combat. Not in preparation of combat. I also think that if one leaves combat they should have to use the command again when reentering combat.
If it is decided that holding something in the other hand while fighting with a single handed weapon is overpowered, one could add a slight penalty when in this situation. Further, if one felt this was too much, one could have the command take a combat round to employ, thus impacting your attacks.