My first reaction to “Acorns are poisonous” was “Well, that´s bullshit”. I spent my childhood stealing them from the neighborhood squirrels and enjoyed them as a healthy snack for years. After consulting with the interwebs, I found out that in large quantities acorns can cause an upset stomach. Not quite the same as poisonous, yet good to know!
Acorns are rich in protein, vitamin B6, and fat and thus make the perfect wilderness snack. Although you can pick them green, you should wait for them to turn brown before eating them. Make sure that the acorn is free of any imperfections as this may indicate the presence of insects. Also, don´t literally steal a squirrel´s acorns. Instead of plugging empty an entire tree, take a few acorns here and there.
Depending on the type of oak tree you gather from, Acorns are more or less bitter in taste and thus you may wish to further process this nut as illustrated on this website. Personally, I enjoy them raw, but there a ways of making acorn flour, spread, and even coffee! Additionally, by boiling acorns in a particular way, one can even take bitterness out of them.