Given that civilization has collapsed, I would not expect them to be using potatoes for silencers if only because they'll probably need them for food. Silencers would be good...though they still make a noise and we have no idea how zombie "hearing" works.
As for the crossbow, how good are those with head shots? A crossbow may not do enough damage to the brain to be effective. The other problem with the crossbow is the limited amount of ammo that you can carry at any given time...especially compared to a gun. Cross bows are great for distance shooting and sniping but in a street fight give you'd be better off with some form of automatic weapon.