One of the greatest fears that people have with the undead is they might get caught in a situation where they don't have their primary or secondary weapon with them. I know, it happens. This is where situational awareness goes to a new level.
Suppose you're caught in an alley and the Z is blocking your exit? You've got no weapon and its fresh enough to get hold of you if you try to get around it. What to do? Well, I like to think of the world as my weapon, that there are enough things out there to do enough damage to get yourself away to get your primary weapon if you need to finish the little nasty off.
When the zombie comes at you, stay focused and ready to explode into action. Zombies don't adapt well, they are typical plunge in and bite types. When the arms come up, (and they will) lean to either side and grab the zombie's wrist with your closest hand. Pull the ghoul forward, placing your other hand on the same arm, right above the elbow. DON'T grab because your fingers could get bit. Push with the elbow hand and pull with the wrist hand. The zombie will follow your lead, but only for a couple of seconds. Use those seconds to SMASH said zombie's head into the nearest wall.
Repeat as necessary. No weapon needed.
Reminder: This only works with really hard objects to slam Z heads into.