Poncho or similar - in a real wilderness situation getting shelter is issue one, and you'd be best to assume it's wet, dark and you are injured. Getting out of wind/rain until dawn or rescue is priority one in a lot of cases, so something I can wrap myself in or crawl into would be best (even the hated space blanket would be better than nothing)

That said I consider a small knife, lighter and torch to be the edc trinity. And frediver has the correct on a cook pot - valuable and hard to improvise