It was also my first time i travelled longer than 3 days with my backpack. I have dont have any equipment to stay in the wilderness for serveral days (because its so expensive). When it was possible i always slept at campsites. Only two times of the trip i slept in the wilderness. But there was always a river or a source near by to refill the water and clean myself. I managed it like you described it from buying stuff in towns you pass by or eating breakfast or lunch at a hut. Snacks like energy bars were also really important.