Mix the corn chex, rice chex, wheat chex, pretzels, pecans, and cashews in a large plastic bag. Divide mixture into two 1 gallon roaster pans and set aside.
In a large saucepan, over medium heat, combine the butter, oil, worcestershire sauce, celery salt, accent, allspice, cayenne pepper, and garlic powder. Stir well. This does not need to come to a boil. Just stir and heat.
Add the seasoning mixture to the dry mixture and blend very well. Cook at 200 degrees for 3 hours, stirring every 30 minutes. This yields 4 gallons.
NOTE: I found that using a Nesco or other electric roaster pan works just as well. I mix all the dry ingredients in that and then stir in the wet mixture.