Preheat the oven to 250 degrees F (120 degrees C). Melt butter, Worcestershire, garlic salt, and celery salt over low heat in a medium saucepan until butter has dissolved, 3 to 5 minutes. Combine rice cereal, wheat cereal, corn cereal, oat cereal, mixed nuts, and pretzel sticks in a large mixing bowl. Pour butter mixture over and gently stir to coat all of the pieces. Transfer mixture to a large roasting pan. Bake in the preheated oven until golden, about 2 hours, stirring gently every 15 minutes. Remove from the oven and let cool completely, about 1 hour. Store in airtight containers.