The direct answer to your question is No. I do not know the size of our planet's food reserves.
I doubt that anyone else does, either. You would have to specify whether you mean "food reserves at current rates of consumption" or "food reserves at the minimum required to sustanin life", or something in between.
Also, you would have to specify whether you mean "food reserves if present production remains unchanged" or "food reserves with all-out efforts to increase annual output" or "food reserves if all agriculture were stopped"; or anything in between.
Then you would further have to qualify your question as to whether it includes all of the food in the oceans -- fish, other marine life, seaweed, marine life not currently harvested, and so on. And you would further have to qualify the question to include all non-human animal life on the planet, regardless of whether it is currently harvested for human food. And you would need to specify whether you include birds, grubs, worms, insects, flowers, fungus, and many other forms of potential food which are not now eaten, or eaten in very small amounts.
If you are hypothesizing nucelar winter, with no agriculture anywhere, all creatures and plants in nature quickly dead, the oceans inaccessible, and nothing to eat except what is currently in storage, the answer is also problematic. Stored foodstuffs are not equally accessible to all people; and hundreds of millions would starve, while people elsewhere had significant quantities of stored food. Distribution would be a major issue, as it is now.
Further complicating your problem, not all of the stored food would survive in a nucelar winter. Refrigeration systems would cease working, as power plants shut down. Frozen meat might be preserved by the external cold, but all stored fresh fruits and vegetables woule quickly become inedible.
Also, much stored food needs to be processed before it is edible; and that might not be possible during a nuclear winter. Potatoes, for example, must be cooked to become digestible. Wheat can be eaten in its natural state (if hulled), but it provides less food energy than when milled and baked into bread.
Candy, you can do better. This is an example of a question that is easy to ask, but impossible to answer meaningfully. Please try to recover your usual focus and incisiveness.
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