Subsistence farming sucks for grains and similiar things that can be efficiently machinized.
For many fruits and vegetables farming still relies on a lot of manual labor, often done by immigrants and vulnerable people under terrible working conditions.
My parents grow most of their fruits and veggies for half a year on about 40 m2 which is a tenth of an acre.
So with very little land it is possible to replace a lot of your grocery bag with self grown produce.