Oddly enough broad beans, squash, sweetcorn and sunflowers (Jerusalem artichokes) were exactly the types of crops that I had considered myself already.If you google there are edible cover crop mixes that may be a good starting point then you could add some of your own seeds like a hardy broad bean, perennial kale, a robust edible squash and even a short sunflower. With all the forage maize grown around us this year I'd like to track down a hardy sweetcorn that would grow readily without much care.