Try the best recipe, which tastes great: mix and apply liberally, and bring extra to apply throughout the pub crawl! Warning - This stuff is sticky! Take a few drops of laundry detergent or dish soap, it might not taste quite as good, but it won't glue your hair to your clothes if you put in some soap.
Fake Scab Recipe
1 part Gelatin
1 part water

Mix in small quantities, and apply to skin within 30 seconds. It will harden to form a decaying flesh texture. Don’t forget to do this before putting makeup on!
Fake Flesh Recipe:
2 cups Self-Raising Flour
1 cup Salt  
4 teaspoons cream of tartar
2 cups water
2 Tablespoons cooking oil

First of all, boil the water, add everything but the flour, and add the flour slowly, over low heat. Cook until it becomes a warm doughy ball. Then form this into rotting flesh slabs to adhere them to your face with liquid latex (ideally), or fake scab mix. It makes great scars, gashes, and decaying flesh, and this stuff has been tested.