My family needs food though. Perhaps a supermarket is a poor example. I think people might purchase fewer luxury goods in a deflationary world which TBH I'm not sure is a bad thing.

To put it another way, the model you're presenting reads well in an economics textbook and I'm sure is exactly how we justify our MMT social policy but it doesn't fully account for actual human behavior. I'll buy necessities (house/food/water/electric/communication) even in a deflationary economy.

When was the last time you went to the grocery store and thought "I better buy this milk today because my money will have less spending power tomorrow"?