In a large mixing bowl, combine the Corn Chex, pretzel twists, Rice Chex, Cheerios, and the Valentine's M&M's.
In a microwave-safe bowl, add the white chocolate chips and 1 and 1/2 teaspoons of vegetable oil. Microwave for 30 seconds. Stir, and continue to microwave in 15-second increments. Stir each time until the chocolate is melted and smooth.
Pour the melted white chocolate over the snack mix. Stir quickly to ensure all of the mixture gets coated evenly.
Line a large baking sheet with some parchment paper. Pour out the snack mix and evenly spread it on the baking sheet to cool. Sprinkle with Valentine's sprinkles if desired. Allow the chocolate to cool completely, break the mix into pieces and serve.