Silk scarves have provided the best play- they are sarongs for DD, wraps for dolly, bed linen, veils, wings, 'rivers' for DD to swim in- it goes on and on!
Also, DH picked up a roadside branch, sawed off pieces of diff sizes and sanded them. Well!! These have become people, plates and cups, playground equipment, animals, fences, chairs for small toys etc etc And completely free!
DD also loves her real (from the Salvos) muffin tins, cake tins, spoons, sieves etc in her sand pit.