In a large mixing bowl, combine the rice cereal, popcorn, pretzel sticks, M&M's, and dried cranberries if using. Toss gently to mix.
In a microwave-safe bowl, melt the white chocolate chips with the vegetable oil in 30-second intervals, stirring between each until smooth.
Drizzle the melted white chocolate over the snack mix and gently stir to coat the ingredients evenly.
Spread the mixture onto a baking sheet lined with parchment paper and sprinkle with sea salt.
Allow the snack mix to cool completely, then break it into clusters and store in an airtight container.