This is a technique for getting to the 50-day achievement. It's not exactly fun, but it is somewhat realistic. It relies on using (or abusing) two beneficial systems in the game: the slower rate of calorie use while sleeping, and the rapid healing process of sleeping with food in your belly. Think of it as very careful rationing.

Edit: This hasn't worked for quite some time; it was useful to get the achievement back in the earliest of early access days, but the game has changed a lot in the decade since.

This is probably easiest to do on Coastal Highway, as scavenged food is more plentiful there. Be wary of wolves; they will be your main obstacle.

• Lots of food. You'll need roughly a granola bar per day.
  
• Water. You'll be drinking about 1.5L per day.
  
• A can opener (or knife or hatchet). This will be a lot harder without one, though not impossible.
  
• A hatchet for firewood. Again, a lot harder without one, though not impossible.
  
• A house with a bed and a fireplace.

Before you start hibernating, make sure you have ample water. You'll probably need to boil a bunch of snow before you start, which means you should not be starving yet. Boil about 1.5L per day you'll be hibernating. You can safely do this over reclaimed wood, though if you like your base and want to keep hibernating there you'll need to gather outdoors eventually.

Next, start sleeping in 8 hour blocks, while deliberately starving. Make sure to stay hydrated! Don't eat; you are relying on your condition to offset food intake. After you begin starving, you'll lose about 1% condition per hour of sleep. Starve yourself down to around 25% condition, which should take about three days. Then, eat a single food item, drink water and sleep another 8 hours. You'll heal because you are fed and hydrated, at a rate of 5% per hour, much, much faster than you lost condition. If you ate a can of pork and beans (an easy example because 600 calories = 8 hours sleep), you'll heal +40% condition, enough to starve for another 1.66 days.

Using this approach, you don't need anywhere near 2000 calories per day. About 360 per day is sufficient. A 1kg block of venison will tide you over for almost three days. A single house's food is enough to survive 10+ days, if you are lucky.

This all falls apart if you forget to drink water. It's somewhat monotonous to sleep your way though the game, so it can be easy to forget to drink water. Once usually won't kill you, but if you forget to drink water on the rare occasion that you are eating food, you will waste the food. This is because you only heal when you are both fed and hydrated.

The first few hibernation periods, you'll probably run out of water before you run out of food. Make sure to leave yourself enough food and water to heal back up to 100% condition before venturing out to collect more food and firewood to boil water. Both of these are strenuous activities, unlike sleeping, and you need to be in good condition in case you are attacked by a wolf. Keep a healthy buffer in case you have to sleep an hour to make a wolf go away...