Mix corn cereal, wheat cereal, rice cereal, cheese-flavored crackers, and pretzels in a gallon-sized resealable bag; seal and toss to mix.
Stir butter, barbeque sauce, Worcestershire sauce, onion powder, garlic powder, and salt together in a bowl. Pour half the butter mixture into the cereal mixture; seal bag and shake until well combined. Pour remaining liquid mixture into cereal mixture; seal bag and shake until cereal mixture is well coated. Pour coated cereal mixture into the slow cooker.
Cook on Low, stirring every 15 minutes, for 30 minutes. Turn temperature to High and cook for 15 minutes. Stir and cook uncovered until coating has cooked into cereal mixture, 20 to 25 more minutes. Spread party mixture onto a baking sheet until cooled and dried.