This can result in sprained ankles, torn muscles and broken bones. Trail running with an existing injury can exacerbate that injury because of the twisting, uneven trail and hilly terrain. I've actually encountered runners going in the exact opposite direction than they thought. For runs over one hour, adding about 100 -200 calories carbohydrate every 30 minutes keeps blood sugar and liver glycogen levels high enough to give you energy to keep running. To run on trails, you need to use your best shoes with heel stability, forefoot flexibility and cushioning because of the unevenness of the trail.
Many manufacturers make trail shoes which have the characteristics needed for trail running.
The traction of trail shoes in mud or soft dirt makes them invaluable. There are lots of ways to carry stuff, the most popular being the fanny pack. If you're not familiar with the area, take a map and compass. If I'm going out in the wilds, I fold up a marathon blanket and stick it in the bottom of my pack along with a small first aid kit. The gels and bars are good sources, but need water to get to the best concentration to be absorbed.