Reliable food and water sources are paramount for long-term survival. While canned goods are great for emergencies, you'll need sustainable options. For water, locate a well in a town. Wells provide unlimited clean water. If no well is nearby, find a river or lake. Fill empty bottles, then use a 'Campfire' to boil the water (requires 'Wood' and a 'Lighter' or 'Matches') or find 'Water Purification Tablets'. Drinking unpurified water will lead to 'Cholera', a debilitating illness.
For food, hunting is a viable option. Deer, rabbits, and boars can be found in forested areas. Kill them with a melee weapon or firearm, then use a 'Hunting Knife' or 'Machete' to 'Field Dress' them, yielding 'Raw Meat'. Cook raw meat on a 'Campfire' to make 'Cooked Meat', which provides more sustenance and prevents food poisoning. Farming is a later-game option, requiring 'Seeds', 'Fertilizer', and a 'Hoe' to cultivate plots near your base. This provides a renewable food source but requires significant initial investment.