In a separate bowl, whisk together butter and salt until the salt is dissolved. Stir in the Worcestershire sauce until combined.
Toss the sauce with the cereal mixture until well-combined.
Cover and cook on low for 3 hours, stirring 45 minutes into cooking time. When done cooking, spread evenly on a lined baking sheet to cool. When cooled, mix in M&Ms or popcorn. Store in airtight containers or serve right away.