As mentioned in the comments, you need to do the following steps after you beat the introduction level (lab / pre-outbreak).
to make this clear, when you spawn in the coffin near the city this is the place where you need to do the following:
If you are having trouble with this, you should use the mutators for no hungry and not damage. and then go to the mall where you can neat around 20 pieces of food.
In the area of the beach were is the penguin statue you can find another 10 pieces of food.
And the rest you can find them in the barn (to the left of the hole you can find some vegetables in the ground.
if you still need some more food you can craft sugar and an item, but you must likely will found them around every place like for example:THE IRISHMAN 35:Another really good place to get food is when you spawn. If you turn around you face the 3 cages. There is an orage house with a burned out car in the driveway on the right side. Go upstairs and you will find a room in the far right hand corner and it is filled with food. It has maybe 20 pieces of food in thereCalex dEUS:Circus has 2 booths with about 10 food items in each.
Just my recommendation is to avoid death (use mutators) and don't be to reckless (like falling with an objec [money] from the roof of the mall to the parking lot) because it's probably that you can make crash the game somehow, and will need to start again, TESTED... twice)