In a heat-proof bowl, combine the butter, chocolate chips, and peanut butter together. Microwave at 30-second intervals, stirring after each, until melted and smooth. Remove from the microwave and stir in vanilla extract and salt.
Add rice and wheat Chex to a large bowl and gently stir them together, then pour the chocolate peanut butter mixture over the cereal.
Gently stir until the cereal is evenly coated in the chocolate.
Allow the chocolate to cool down slightly (but not harden).
Add powdered sugar to a gallon-sized ziplock bag. Then add the chocolate-covered Chex. Seal and shake the bag gently to evenly coat the Chex with powdered sugar.
Spread the puppy chow out onto a baking sheet and allow it to cool and harden. You can speed up this process by placing the tray in the fridge. If needed, break up any clumps.
Before serving, add the puppy chow to a large bowl. Mix in peanuts, M&Ms, mini pretzels, and mini Reeses cups.