No real fears, more like concerns. There is a saying in ultralight backpacking circles that you "pack your insecurities". In other words whatever you pack a lot of is where your concern lies. I pack a lot of water/electrolyte fluids (3-5 quarts), food (2-3 high calorie sandwiches, 4-5 clif bars, trail mix), and a great headlamp. So, I'm always hoping I have enough food, water, and daylight or battery life to get home. Especially the food and water, I've found that the better the shape I'm in, I can just keep going as long as I have food and water. Conversely, if I run out it can turn into a real forced-march type thing.