Just a quick guide on how to get to day 500.
As you probably know already a lot of luck is needed for this game. A good strategy to increase your odds of survival is to do the following:
-use up your bullets on zombies for items and added health bonuses (holding on to bullets and health is waste, especially when you can lose all of them through a couple of encounters with the super Zombie), at least, early on when your melee weapon does little damage.
Use health kits to heal you when you're down a few points, but never use the "rest" feature - it's a waste of time.
Always try to have at least 10 food items in stock, and always be out searching for more. Also, make sure you have scouted out 4 areas where you can search. If you have 0 food, you can't use the scout feature, no matter how much health you have.
Early in the game it is easy to get 20 or more food items. Use the excess food to build up your health through the "workout" feature, but try not to go under 10 food items.
Don't be afraid to flee zombie encounters when you have no bullets, and your melee weapon does very little damage to them. Later, when you can destroy them with 2-3 hits with you melee weapon you should try to destroy as many as you can for food and health bonuses.