Not for fun. In SERE-C (NC in January) I went seven days with just a handful of wild onions, a bowl of rice, and two sardines. I was deprived of sleep for a few days so that plays into the following experience.
End of the course I dropped >20lbs. Hunger pains disappeared after the first couple days but I was plagued with fatigue throughout the week. You'll burn through the glycogen fairly quick and the brain is quite fond of glucose; fish will obviously not replace your carbs. Brain function will deteriorate and I started having difficulty completing mundance tasks. After the completion of the course, I had difficulty using my calling card to call my wife. As this was training, if I would have had a real life or death emergency, help was not too far away.
In the winter your body becomes a calorie burning machine to keep warm. Starving it of fuel only compounds the problem.
I'm a big fan of developing mental toughness and living off of the land but I'd only do this in a controlled environment which does not involve complex land navigation. Pack some food but only use it for emergencies. 'Into the Wild' is certainly similar to this topic.