We as a nation should provide lunch to every student legally required by law to attend a public school.
Students who are required to attend should have basic human needs during those hours fulfilled. We provide water fountains, and restrooms to students, lunch is no less of a basic human need.
We have ~50 million students required to attend by law according to the center for education reform's website. (http://www.edreform.com/2012/04/k-12-facts/)
The average school lunch provided to students costs $3-5(as a high estimate).
If we multiply this cost, against the number of students we receive a rounded figure ranging from a low of $150M to a high of $250M for providing a lunch to every student, poverty stricken or not.
This is a mere 1.3% increase to the food services budget.