Single-use pocket and hand warmers
You can find these products in countries like Japan, Taiwan, and South Korea. These pocket-sized hand warmers are called kairo, which is a bag of chemicals that warm your hands during the winter season. To activate the chemicals, just give the bag a quick shake, then place it in your pockets. Whenever your fingers get cold, just play around with the bag.
You can find kairo bags in every 7-11 store, and there are 20,000 7-11 outlets across the country. Each bag can provide up to four hours of moderate heat. After using them up, simply toss them in a trash bin.