Line a 9x9-inch baking dish with parchment paper.

In a large mixing bowl, gently stir oats, cereal, chocolate chips, and M&Ms. Set aside.

Melt honey and peanut butter together in a small saucepan over low heat, whisking to combine. Remove from heat once smooth and stir in vanilla. Pour over the oat mixture and gently toss to coat.

Press into the prepared baking dish, using a good bit of pressure but not crushing anything. Refrigerate for at least an hour before cutting.