I tend to disagree with needing two Earths to feed the population, though I agree that the amount of food being wasted is atrocious and unneeded. If farmers were to be encouraged to produce more staple foods and received more (fertile) soil, instead of being bullied by big agrarian businesses, it would greatly help. Then there's other elements that cause trouble such as Monsanto and their GMO terminator seeds.
Encouraging people to have their own gardens and make sure people are able to have such gardens (by improving zoning) could help a lot as well. A few city ordinances could greatly assist with that as well.
Quite some parts of the planet aren't being used for production or to live on, which does limit the total capacity we're able to use. If such could be expanded in a careful manner without hurting the local ecologies that could sustain another few percentages of the population.
I tend not to expect things to improve much with the current leadership in the world though. Until monopolists and power brokers are kicked out of places of power you can expect food, water and even air to be used as a weapon against people, if not now, then in the future.
I also want to add that we're more likely to see lack of food due to distribution and supply rather than actual production. The moment people start panick buying food because of an imminent crisis, for instance, is when the stores suddenly will be emptied, and that supply cannot keep up.