Mice are mainly omnivores and herbivores, depending on where they live, and some are carnivorous if no other food source is available. Mice are very opportunistic eaters, so they normally feed on whatever is most readily available in their environment.
Vegetation is the most common food for mice in nature, along with seeds and fruits that are indigenous to the area. Roots, tree bark and other available vegetation are also on the menu for most mice because they are herbivores. Some mice are omnivores, including the wood mouse, and they'll snack on worms, crickets, snails and centipedes if given the chance. No matter where they live, mice will feast on whatever leftover scraps they can find in dumpsters and garbage cans.