The real, edible flesh leg will have trick-or-treaters gagging as the zombie tears off chunks of rotting meat and eats it.
Leg is made by cooking a meatloaf in a large round soup can with a rawhide dog bone in center. (Do not eat dog bone) Cooking meatload with spinach will give it a vein-y look. Fake, black blood will add to the effect (chose an edible kind, or use blood pellets that can be broken in mouth)
put cooked meatloaf and bone in top of a clean pair of denim jeans. Stuff leg with filler and add shoe to the bottom.
Zombie makeup uses latex and fake blood for wounds and scars. A bit of skull makeup showing up underneath can enhance the effect. I bought some zombie contacts to deaden the eyes, but those can be expensive. Rest of the costume was negligible cost if you have already have basic halloween makeup