Grand jury is so named because traditionally it has greater number of jurors than trial jury, called a petit jury (from the French word petit meaning small).
Although mice tend to come out in the night when most of the occupants of the house are asleep or immobile. This allows them to stealthily infiltrate any of your food bags, crumbs etc. During the day time, mice will normally not come out, but if opportunities exist then they surely can.
Mice are omnivores and eat a variety of foods preferring seeds, grains and nuts. They require only about l/10 ounce of food each day and can live without access to fresh water if the solid food they eat is somewhat moist.