Often I use natural and waste materials like glass (bowls, glasses, jars), bins, lids, tins and cans.

 
 
 
 
 
 
 
 
 
 
 

The Bathing Baby is made of a broken bowl, the tree-stump in Sleeping Time was made using a tin can, Mr Mole was made of a circle of cane.

For creating eyes I often use black clay, but you can also use dolls/bear eyes (of glass, otherwise it may melt) or beads. With a toothbrush or a piece of cloth (put it around a glass and roll it over your workpiece) you can create patterns.

Polystyrene balls
They can be bought in several sizes and used more than once. How?
Make a foundation of your choice and cover half of the ball with clay. Put this on your foundation (with the opening in front or up, it's your choice) and decorate as desired. Bake this. You will see the ball will shrink and is, therefore, easy to extract. Now you can decorate the insides of your hollow or cave. The ball itself can be used as the insides of another workpiece. Please make sure that you cover it first with aluminium foil, otherwise it may collapse under your workpiece.
 

To personalize your workpiece you can add your initials or a stamp.

Books
There are a lots of books to be found in book shops and libraries. Take your pick and experience the wonders of polymer clay.