Line a sheet pan: Line a large rimmed baking sheet with parchment paper and set it aside. This makes cleanup easy and helps the mix lift off in one piece once it sets.

Combine cereal and pretzels: In a very large bowl, combine the Corn Chex, Rice Chex and mini pretzel twists. Toss gently so the pieces stay whole.

Melt the white chocolate: In a microwave-safe bowl, combine the white chocolate chips and vegetable oil. Microwave in 30-second bursts, stirring between each one, until smooth, about 1 1/2 minutes total.

Stir in vanilla and color: Stir the vanilla extract into the melted chocolate. Add the orange gel food coloring if using, and mix until the color looks even throughout.

Pour over the dry mix: Pour the melted chocolate over the cereal and pretzels. Fold gently with a rubber spatula until every piece is coated, working quickly before the chocolate firms up.

Spread onto the sheet pan: Spread the coated mixture in a thin, even layer on the prepared baking sheet. Spreading it out helps it cool and harden evenly rather than clumping together.

Add the candy: While the chocolate is still wet, scatter the candy corn, candy-coated chocolate candies and Halloween sprinkles evenly over the top.

Let it set: Let the mix sit at room temperature for 15 to 20 minutes, or in the refrigerator for about 10 minutes, until the chocolate hardens and loses its shine.

Break apart and serve: Once set, break the mix into bite-size clusters with your hands. Serve in a large bowl or portion into small bags for trick-or-treat giveaways.