Chop the side off an old shoe box and decorate the outside with bits of twigs 'n stuff to look like a stable; scrunch up strips of paper (painted straw colour) for the floor - or used that stuff packers use, shove in a few toy figures and animals, stick a star on a length of wire over the top and there yer go! Instant Nativity scene ;D

Plasticine makes good figures too, if you or your kids are feeling creative :D

Nothing beats a Christmas Crib scene which has been made by children.