Where I live, in the wild areas, there are berries, mushrooms, dandelion leaves, wild rice (grows wild in certain lakes and streams up here), pine nuts, and chestnuts to name a few foods.
If one is planning to go on a wilderness trip, it is a very wise idea to prepare ahead in every way possible. This would include knowing what kinds of wild plants are available in the wild there, and weather patterns/conditions, terrain, etc. Maps are crucial, and compass skills, and the ability to start fire with what nature has to offer. You also have to consider encounters with wildlife in the area, and the possibility of your food being taken. I have done some Boundary Waters Canoe area Wilderness (BWCA) trips in NE Minnesota, six in all so far (my partner also did two solo trips). We go about ten to twenty miles into the BWCA via canoe and camp for a week. We prepare well in advance and pack our food in "bear barrels" that are hard and have complicated locks on them and can be hung high from a tree. We bring ropes and pulleys for this. Yes we still have encountered bears in camp and moose. Thankfully they did not take our food, and yes a bear can still get through a "bear barrel". This is why we never go more than a day's paddle/portage from our vehicle. There are no trails or roads in the BWCA, aside from small portage trails between lakes. You carry everything in yourself, so you learn to pack light and stick to essentials.
There have been a handful of lost wilderness campers up here in the BWCA and Canadian Quetico park that extends beyond the BWCA. A few of them survived weeks of being out there with nothing, and they didn't have time to hunt animals, nor the tools. They ate plants they were familiar with, but most of their time was spent figuring out how to keep warm, find shelter (in trees etc), and navigate the wilderness. Another smart idea is to make sure people know where you are going, how long, etc. Exact details.
My partner and I had one situation in 2006 where we were heading out of the BWCA and came on a storm. We still had three large lakes between us and our vehicle, and plenty of wilderness to navigate. It was early May and still cool and we didn't see more than two other parties the entire week we were out there. The temperature dropped into the low 40s F that day and the wind kicked up the waves and it started sleeting while we were paddling. The white caps on the lakes became too dangerous to navigate safely and the water too frigid to risk tipping, so we had to wait it out in a makeshift camp on a smaller lake. We had only brought enough extra food for one more night, and only one more night of our meds etc. The next day it was still stormy but thankfully not as fierce or wet and we were able to get out, but it was a good lesson for us to be more prepared next time.