I've recently upgraded and modified the emergency gear kit I always carry when I hike or backpack. It may seem like overkill until you turn an ankle on what should have been an easy day hike, the temperature is dropping, and you are facing a night alone in the woods. My kit weighs several pounds and fits into this small orange bag:
Do you think I am missing anything critical? One thing I should add is a PowerBar as an emergency food source. We can survive a long time without food, but a little something to eat can calm you down in a stressful and scary situation.
I'll be fine-tuning my kit now and again as I learn more and think about survival situations. By the way, I always carry a separate first aid kit any time that I hike.