Welcome to permies.com Damian!
I advise going to the
Plants For a Future Database and entering your hardiness zone and soil type (light/sandy) for a general search of what could potentially grow in your area. Then, add on whatever other filters you need so that you can find what you are looking for. You can find your plant hardiness zone on the
USDA website or from the image below:
One very delicious plant that could add organic matter to your soil and provide tasty food for you is
sea buckthorn:
I think another place to look for information about growing plants in your area would be the
Edible Landscaping Guide by the University of Florida. They do list adding organic matter onto site, initially, in one of their sub-articles, but that could be replaced with cover crops that you find and like
online.