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.
It might be useful to subdivide that list of perennial edibles into calorie-dense and nutrient-dense foods. I could give it a try.
The other think you could think about is that "Food Forest" doesn't mean "No Annual Vegetables". They are extremely important in the beginning phases, and in later phases the number of seeds in the ground could be enough (from previous annual culture) that you might find volunteers, or "patches" of stuff you didn't directly plant. Or you might just put annuals in every time you disturbed soil, just to move things along.
The idea is that you'd be getting annuals, but you wouldn't be sweating over barren soil hoping for them to come up. They would just be filling their (smaller) niches naturally. Sure, the wild forms are smaller and perhaps more bitter, but since you're eating from the forest, you're not really concentrating on growing that 5 pound juicy tomato. The game is just different.
At least that's my take on the annual's place in a food forest.
Theporblem I see most of the time with forest gardens is lack of diversity in annuals. They are just as important as the perennials IMO. A diverse forest garden should have patches of annuals, patches of perennials and spaces with a mix of both.
The ultimate goal of farming is not the growing of crops, but the cultivation and perfection of human beings. - Masanobu Fukuoka
I agree with William, regular annual vegetables play a role in the beginning of a food forest, because you want to be able to grow something in the full sun you're likely to have. And even later on, if you plan to have some sunny spots, you can keep growing normal annual vegetables in the food forest, just not in the super shady parts.