One great way of cooking food when you only have a fire to go off of is to wrap it in tin foil and toss it in the fire.
You won't be finding tin-foil in the woods, though! Instead, there's a leaf you can use: burdock. Just wrap up the food in 3-4 layers of burdock leaves and it will cook just like it's wrapped in tin foil.
You can also use the leaves as an improvised container or bowl for gathering things like berries. You can also use cabbage leaves, dock leaves, mallow leaves and banana leaves.