How do I get the frozen pizza at Gervacen's Grocery store?

You have to enter the freezer and crawl through it, the WHOLE thing. Which is a challenge in itself.

To start with, you'll be working your way from right to left behind each freezer door, until you come to a row of shelves. You'll want to slip one foot onto a shelf, then lift the other over the top shelf, then slide the other foot through to the other side.

THEN you'll need to slip through the empty shelf, which the game will help you out with by making your body go limp while crawling through it.

This will then lift you into an air vent, which should take you right to the frozen pizza.