There are lots of great books that introduce the idea of symbolic play. One example is Baby Bear's use of everyday objects to travel to space in Whatever Next? This is a lovely bedtime story, full of adventure. Read the story to your toddler on several occasions. When they are more familiar with it, read the book at a time when your toddler is awake and alert. Pop out some of the items that baby Bear uses for his imaginative play in the book. Notice whether your toddler makes the link between the story and the items. You might be surprised to see them using the items like Baby Bear did, or they might have their own creative ideas.