I strongly agree with the winter rye sentiment at this stage. I would not hesitate to mix in a modest amount of radishes, but I would not mess with oats at this stage. They will die at the first frost and you may only get 10-20 days of them in late planted fall plot, but that is just me. Clover is fine, even a good idea, as long as you know that you will not have much, or any, clover growing there this fall, it will come on early next year though.