Maybe we should spend time assembling dietary suggestions based on wild foods for long term survival. I believe even the FDA has tables of the nutritional value and contents of many wild foods.
Excellent idea!
I keep a single multivitamin tablet in my PSK.
Here are some sources I know of for a few vitamins that were mentioned:
Vitamin C: needles from many nontoxic coniferous trees (chew them or make a tea) I've munched on pine and hemlock myself as a trail snack. If you want to know what it tastes like, take a big, concentrated whiff of your live Christmas tree, and then imagine eating it.

(Please, don't eat your tree until Christmas is over!

)
Vitamin D: sunlight on your skin (10 minutes/day), eggs
The internal organs of animals are often high in vitamins, but some are high enough in concentration to be toxic, so be careful.