Vladek makes a huge fuss about matches and salt, even though they are very inexpensive. Why is this so important?

Vladek's obsessive hoarding is a constant motif through the story. Vladek continually had to scrounge for necessities during the war: there was always a scarcity of things. There was the constant fear of not being able to light a fire or not having enough salt to keep food from spoiling. In peacetime, Vladek cannot stop his compulsion to hoard these items even though they are plenty.