For your character not to die of hunger and thirst, you have to watch their condition carefully in order to refill these stats in time. At first you can eat canned beans you find, obtain raw meat, fish and berries. But when you make Campfire, Meat Dryer and Kitchen Stove, you’ll be able to cook more nutritious dishes. You can get water by putting empty bottles into Rain Catcher or find it in boxes on locations.
And, right up to level 100 of your character, some water and canned goods will also appear in the "Inbox" section.