Explore the maps, the buildings, gather resources, because every little rock you add to your inventory will matter later on. Another thing to look out for is a backpack. Keep looting until you run into one and that will provide more space for you to keep your stuff in. If you eat raw food you will have a harder time resting and staying healthy, so it is best if possible to have a fire going and cook. You need to purify the water by boiling it before drinking, and that will, too, prevent you from contacting diseases and illnesses.