Pegi: An old shirt and pair of pants would work. You can stuff the clothes with plastic bags to fill out the body. Use an old belt, sash, scarf or even a piece of twine to cinch the waist. If you have pine needles around your area you could stuff the ends of the arms and legs with pine needles and leave a little bit of straw sticking out where the wrists and ankles/feet would be. As for the head, I'm not sure ... I have seen headless scarecrows before but if you have something sticking up above the neck of the shirt maybe just put an old baseball cap or some kind of hat on there and stuff straw around it?
Listen to me giving suggestions ... I haven't even begun this project yet!