In the Kubiki district of Niigata, people have traditionally spread a variety of ingredients such as wild plants or river fish on sushi rice, and then bound the mixture in leaves of sasa bamboo. These long leaves are a convenient wrapping material and also have natural antibacterial properties. The vinegar in the sushi rice helps to preserve the food as well, so the sushi keeps well without spoiling. So sasa-zushi is an especially good food for taking on outings.