Sutherland Kale - eat the leaves or flower shoots. Very tough - overwinters here ! Self seeds so you can just dig up old plants when you get too much.
Nasturtiums will self seed & give you salad leaves or "capers"
Nettles. No kidding - Spring shoots make the best soup ever, very healthy, full of iron & then when they get tougher they make liquid feed just as good as comfrey & if they get really fibrous you can spin them just like linen!