Geese tend to eat grass, seeds, and other foods that would fall into a vegetarian diet. Mostly, geese are herbivores because they eat grass, seeds, nuts, and berries. Sometimes, they could eat insects and fish, but it depends on the type of goose we are talking about. However, it does depend on the type of goose because remember that not all animals are the same. Even if they are from the same family, you are going to find some differences.