According to old Jewish superstition leaving an oven empty will cause one's family to go hungry in the future. To avoid famine, it's enough to leave a baking sheet or a pan in the oven at all times as a precaution.
Cross your fingers - If you look hard enough, you can see this superstition has religious roots. Crossing your fingers is a type of holy protection because the two overlapping fingers form a "slanted cross."