Which is silly, Monsanto doesn't even sell food.
What it does have is market power in the seed market for certain key global crops, and even more in the GM sector (e.g., 80%+ for GM corn, 90%+ for GM soy.)
Monsanto's relationship to food is sort of like 1990s Microsoft's relation to computers.
Fortunately, we don't need those seeds. They can try to patent and sue all they want; the people will prevail.
There are cases where farmers in adjacent plots were sued for using monsanto 'patented' plants without a licence because their crops cross-pollenated with Monsanto ones - further, if I recall correctly, Monsanto was illegally stealing crop samples or using some other form of shady tricks to perform the analysis required to determine the plants contained the 'patented' genes..
Also, much like bacterial resistance in other areas, if the monsanto GMO crops facillitate mutation such that their 'patented' genes are essentially required for a crop to be viable, over the long run, the argument that we 'dont need' the seeds becomes moot..
Probably the main case that comes up is the Schmeiser case, where Schmeiser claims that his roundup-ready canola came from cross-pollination from a neighbor's field. Schmeiser's account does include the fact that he specifically tested the canola in question and found it to be resistant to Roundup--and subsequently used that in later crops. The court concluded that he had to know that at least some of his crop had the GMO canola, and that his deliberate use of it in the subsequent year constituted infringement.