Well first of all he had a plan in place that his sister obviously knew otherwise she wouldn't have been expecting him to arrive by a certain date. Even the information he gave his father was probably very helpful in knowing where would be the best places for rescuers to search for his carcass.
He stuck to the river. He followed the same path of least resistance that water does as it makes its own journey towards meeting larger rivers and eventually to the ocean. Civilization depends on water so it wasn't a far cry for him to assume that he would find civilization at some point either camping alongside, rafting down or driving across the body of water he chose to follow.
He maintained his body core temperature the best he could by reducing the risk of hyperthermia during the hot days, and hypothermia at night. He avoided overheating by dousing himself down in the cool waters of the river and lit himself fires to stay warm by at night.
The river he stuck to was critical in avoiding dehydration as well as providing a route of travel and a way of cooling himself down.
The river also provided a food source for him to stave of starvation with after he overcame the gross factor (if there ever was one for him) and he clearly must have had some knowledge of the wild edibles he could eat otherwise he would have poisoned himself and died riverside from eating Jimsom weed or something else toxic to humans. Frogs and riverside roots are not going to keep you fat, but they will keep you alive and obviously he isn't dead so that isn't doing too bad!
He held on to his lighter even if he did ditch the rest of the gear that was becoming to heavy for him to bare and slowing down his progress back to safety and civilization.
A point commonly overlooked but that is quite valid and important never the less is the fact that he didn't freak out and panic! He kept his damn head on his shoulders! That is quite apparent by the way they described his waving to heli's passing overhead and how he ate his granola bar. People who panic and run off half cocked die more often than you would think, and had he done the same... he would probably be dead as well.
What he did wrong was... he overestimated his abilities and didn't have a way of navigation to aid him, probably from the start.