Some opposition MPs said the new civil defence concept, to go before ministers on Wednesday, was scaremongering, the BBC reported.
Citizens are advised to store enough food to last them 10 days, because initially a disaster might put national emergency services beyond reach.
Five days' water – two litres (half a gallon) per person daily – is advised.
The German news website Frankfurter Allgemeine (FAZ) said the new concept was set out in a 69-page German Interior Ministry document.
The document said "an attack on German territory, requiring conventional defence of the nation, is unlikely." But, it said, a major security threat to the nation in future could not be ruled out, so civil defence measures were necessary.
Interior Minister Thomas de Maiziere told a group of schoolchildren that Germany must be prepared to react if water or food reserves were poisoned, or if oil and gas supplies were interrupted.
The parliamentary head of the left-wing Die Linke party, Dietmar Bartsch, criticised the move, saying "you can completely unsettle people with yet another round of proposals, such as hoarding supplies."
The Greens' deputy parliamentary leader, Konstantin von Notz, said it was sensible to update civil defence advice which had not been touched since 1995.
But he warned against mixing up possible military or terrorist scenarios, saying "I can't see any attack scenario that merits a stockpiling of supplies by the population."
