Pet mice can eat the same type of food that are from the stores that are made for hamsters and Guinea pigs. This type of food should have all the nutrients that they need. They will also eat various different foods such as fruit and vegetables and sunflower seeds. You need to make sure that it does not have salt added. Keep in mind that they can not live off this food as it does not have all the nutrients that commercially produce food will have in it. They need a balance of both.