Acorns and how to eat them.

Since the old times, acorns and wild medlars have been the go-to grain and fruit for poor or isolated people.

According to Galene, the roman successor of Hippocrates:

While acorns have been scorned for many years as "pig's food" it is actually just as nutritious as other grains like weat and rice. Acorns are hard to digest and have viscous juices that can keep you feeling full for an extended period of time, but could also result in indigestion.
To make them edible, one needs to boil or bake them. Often times hunters would hide them in the still burning ashes of their fire and then crack them open. In different occasions the acorns were broken and ground the interior which then was turned into paste with water or milk.

Basically acorns are like a bad batch of chestnuts.

To roast them: Break them into pieces, salt them and either place them in a preheated oven at 370 degrees for 15-20 minutes, or simply over a dry pan (or whatver metal surface you can use) over an open fire. You'll know it's done when they start smelling like roasted nuts, but they don't particularly change colour so be careful.

It can also become a warm beverage similar to coffee: Using roasted acorn pieces, you proceed to brew them in boiling water (one tablespoon of acorn pieces to 8oz of water) for 5-10 minutes.

Since it's grain, you can use it as weat substitute to make bread or cookies, but that would entail drying them and grinding them into weat, which is not something anyone can do in an emergency.