We could start in the US by calling all politicians to stop subsidizing ethanol production to feed corn to cars. The only reason we do it is because Iowa has the early primary vote.

Then, there's the land used for growing corn and wheat that could be used for cannery crops (fruits and vegetables). They used to be, but Corn became King because it takes less labor and you can spray all kinds of chemicals on it to control weeds and bugs (and now, people eat corn that produces its own bug spray, but they call it "GMO" so you don't think about it). Can't do that with most vegetables. Somebody has to go out and find the weeds and kill them with a hoe.