Line a large sheet pan with parchment paper; set aside.
In a very large bowl, combine Corn Chex cereal, mini pretzel twists, Cap’n Crunch, Honey Nut Cheerios, and M&M’s.
In a medium microwave-safe bowl, combine white chocolate chips and vegetable oil. Microwave for 30 seconds, stir, microwave another 25 seconds, then stir until smooth. If needed, microwave for another 10 seconds.
Pour melted chocolate over cereal mixture. Quickly and gently stir until evenly coated. Spread mix evenly onto prepared sheet pan.
Let snack mix harden at room temperature or refrigerate until firm (about 10 to 20 minutes). Break into pieces and enjoy!