The Question and Answer section for MAUS is a great resource to ask questions, find answers, and discuss the novel.
Vladek was a businessman. He owned a textile factory after his marriage (a gift from his father-in-law), and worked in trading goods in America. His experiences during the war taught him to work with what he had.
The Nazis have stripped the town of whatever food they can carry. Vladek and Shivek, however, are able to locate an abandoned home where they find milk and chickens. They hide there, subsisting on the little food left behind.