In a VERY large bowl (or two medium bowls), combine the first 6 ingredients. Set aside.
In a microwave safe bowl, heat white chips and oil on high for 60 seconds (you could also melt chocolate and oil in a double boiler pan).
Stir and microwave for another 30 seconds and stir until completely melted and smooth (you may need to microwave for a couple more seconds).
Pour melted chocolate over cereal mix and stir until all the cereal is evenly covered with white chocolate.
Spread cereal mix on 2 large baking sheets (I used cookie sheets) lined with wax paper.
Let cool and then break apart into chunks.
Store in an airtight container.
Notes
You can swap out the M&M's and the candy corn so that this recipe will work for any holiday. You could also use peanut butter M&Ms for a different flavor.When melting the chocolate in the microwave, mix frequently. Microwave it in 20-30 second increments, stirring it every time you remove it from the microwave. At first the chocolate will still be in its form, but with each time increment, it will soften and melt. Continue to stir until it's smooth.