I'm a big fan of play dough. It supports children's play and development in so many ways and it's really cheap and easy to make. You can do so many things with play dough. Role play games such as making cookies and cakes or other baking/cooking; experimenting with different textures, smells, colours (you can make the dough more interesting by adding extra ingredients to the recipe); molding new shapes also helps children develop the muscles they will later use to hold a pencil and write.
Here's a nice easy recipe for playdough. This is quite a large quantity. 3 cups water; 3 cups plain flour; 1 1/2 cups salt; 2 tbsp cream of tartar; 3 tbsp veg oil; food colouring of your choice. Put everything in a large pan and over a low heat and heat gently until stiff. Knead on a clean surface until smooth. Done!