Do you know ways on how to apply ';conservation of mass'; in our daily lives?

our prof is making us do this report about our experiment on conservation of mass. do you know any activities/ways/applications wherein the concept of conserving mass is used in our day to day activities..(like a social issue, environmental issue..etc.) ex. experiment on icecream making: featuring ';selecta';/';magnolia';... %26lt;--- something like that... tnx!Do you know ways on how to apply ';conservation of mass'; in our daily lives?
Water may be frozen, melted or turned to steam with zero change in mass. Ordinary chemical reactions result in no change in mass (only nuclear reactions change mass). Burning gasoline (in a car) combines oxygen with hydrocarbons to form CO, CO2, and H20 vapor (ignoring NOx's) and the weight (mass) of the gasoline and oxygen exactly equals the weight of the products of combustion. Eating and metabolizing ice cream does not result in a net change in mass (although a person's weight may change because he does not exercise enough to produce sufficient CO2 and metabolic water).