Whisk together Ranch dressing mix and 1/2 cup vegetable oil in a large microwave-safe glass bowl. Stir in oatmeal cereal squares and next 3 ingredients.
Microwave mixture at HIGH 2 minutes, and stir well. Microwave at HIGH 2 more minutes, and stir well. Spread mixture in a single layer on wax paper, and let cool 30 minutes. Add cherries and candy pieces. Store in an airtight container up to 5 days.
Note: For testing purposes only, we used Quaker Essentials Oatmeal Squares for crisp oatmeal cereal squares, Crispix for corn-and-rice cereal, and Wheat Chex for wheat cereal squares.