LINE baking sheet with parchment paper. Press straws into centers of marshmallows. Place jimmies or sprinkles on plate (one plate for each kind).
MELT morsels in small, uncovered, microwave-safe bowl according to package directions; STIR. Morsels may retain some of their original shape. If necessary, microwave at additional 10- to 15-second intervals, stirring just until morsels are melted. Stir in oil (this will help keep the chocolate fluid).
DIP marshmallows halfway into melted morsels; shake off excess. Roll in jimmies. Place on lined baking sheet. Let stand for 30 minutes or until set. Wrap in cellophane or decorative bags and tie closed to preserve freshness.