If you live in a warm(er) area, investigate the moringa tree. This is one website that tells about them.
You will also find many useful veggies at this site -
Also, you might want to check out Neem trees which have been considered "a village pharmacy" in many countries. Neem is not particularly tasty, nor does it smell particularly good, however it (bark capsules) worked to cure my dog of whatever ailed him when the vet's (expensive!) meds failed. I also like the soap from this website (my favorite is with aloe and lavendar)
If you live up north the kale/cabbage family is good, and mints and basil are great anywhere. Also, you can always sprout seeds - anywhere - quickly. Pumpkin and sunflower are easy to find. Google for others.
Hope this helps!