A basic claim to get food for free or at reduced prices does not exist in Germany.
If you are entitled to unemployment benefit II or to social assistance, you can receive help for your livelihood if you cannot adequately cover your need for food, shelter, clothing, household effects, etc. For the conditions for claiming a living allowance, please contact the Employment Agencies or the responsible social welfare offices in the federal states. Employment agencies close to where you live can be found at www.arbeitsagentur.de/privatpersonen. The responsible social welfare office can be found at http://www.sozialaemter.com/.
Social welfare offices in Niedersachsen: http://www.sozialaemter.com/index.php/sozialamter-niedersachsen
If you are entitled to social benefits, it is possible to get food for Your daily needs at the “Tafel”. Tafeln in Niedersachen: http://www.tafel-niedersachsen.de/ihre-tafel-vorort
Church facilities help as well, if you need help.