Warning: Do not eat any mushrooms that you find on the trail unless you absolutely know how to positively identify the edible from the poisonous mushrooms. There is no point in taking a chance, it is easier and safer to choose not to tempt fate.
What are your options when you are out in the woods without any food? Wild berries are easily identified, they are just a little smaller than the store-bought berries, readily available, taste delicious, or at least some of them do, and are usually high in vitamin food preppers C. Berries that you are likely to find on the trail include strawberries, blueberries, blackberries and raspberries. Try tasting some of those berries. If they taste like what they look like you are good to go. If they don’t taste good, spit them out. The only berries you need to worry about in North America that can poison you from just tasting are poison ivy berries, which are white. So if you are unsure avoid all white berries.
There are a lot of other berries you might want to try including thimbleberries, high bush cranberries, currants, service berries and rose hips to name a few. Get yourself a good book on edible plants to take with you on your next hike. Practice identifying different edible plants in case you might need them in the future.
If there are oak trees around, acorns might be another food source for you. I say maybe because acorns contain tannin and some acorns have more tannin than others. If the acorns taste bitter you might try boiling them. Even after a couple of hours some acorns might still be too bitter to be palatable. If there are chestnut trees around you might try roasting a few. Nuts are high in fat and have 50% more calories than an equal weight of sugar.
The inner bark of pine trees (genus pinus) is edible but may require boiling first to improve digestion. Palatability is another question but when you are trying to survive it can provide a source of food. To get at the inner bark remove bark from the trees and scrap off the inner layer of the bark.
A plant that everyone knows is the dandelion. Dandelions have jagged edge leaves and bright yellow flowers. They grow close to the ground. All parts of the dandelion are edible. You can eat the leaves either raw or cooked and the roots should be boiled like a vegetable. Dandelions are high in vitamin A, C, E, B-complex, iron, calcium, and potassium. The leaves are best eaten in the spring when they are less bitter. Plants growing in the shade and under dead grass are also likely to be less bitter in flavor. The flowers can be tossed into a salad or dipped into flour and fried. The white sap from the flower stems can be used as glue.