Green veggies are the easiest to start with. Stinging nettle is a good perennial green veggie. Buckwheat is another nice addition as you can eat the leaves and of course use the seeds as flour. Buckwheat can easily become an annual "weed" if left to flower and set seed. Varieous squash and mellons can be planted as well and grow pretty well so long as they get some light. Other perennials I'd look into would be ground plums, ground nuts, maximillian sunflowers, sunchokes, nine star broccoli (perennial) and kale to name a few, kale can be a semi perennial or you can try tree kale/collards.