Preheat oven to 250 In a large roasting pan (I get the disposable aluminum turkey roaster pans) stir together the Cheerios, Rice Chex, pretzels and peanuts; set aside. (I always use store-brand cereals, you can't tell the difference here) Melt the margarine and stir in the garlic powder, onion salt, celery salt and Worcestershire sauce. Slowly pour this over the cereal mix, stirring to coat as much as possible. Cover pan tightly with aluminum foil. Bake at 250 for 2 hours, 1st hour covered, 2nd hour uncovered. Stir every half hour. Allow to cool before storing. I usually make 2 pans at a time. Enjoy!