In large microwavable bowl, place cereals. In 2-cup microwavable measuring cup, microwave butter, brown sugar and honey uncovered on High 2 minutes, stirring after 1 minute, until mixture is bubbly. Stir in spices and rum flavoring. Pour over cereal mixture, stirring until coated.
Microwave uncovered on High 3 minutes, stirring and scraping bowl after every minute.
Cool slightly; about 5 minutes. Stir in marshmallows. Spread on waxed paper. Store in airtight container.