If you're one of those people who dreads winter because your hands and feet are cold all the time, what do you do?
Well, if you're Japanese, you probably keep a supply of disposable kairo (懐炉) at your home or office.
Kairo are little packets containing (safe) chemical ingredients that when triggered heat up to 50-60 degrees Celsius (120-140 degrees F) and stay warm for 5-18 hours.
They come in a number of formats, including those that can be affixed to clothing, put inside shoes, or carried around in your pocket, and you can buy them just about anywhere, from the corner convenience store to your local supermarket. A typical pocket kairo costs about 50 Yen (43 cents). The kairo package pictured above is part of the Okamoto product lineup, which includes kairo for medical uses (backaches, etc.) and those to keep your backside warm when when camping, fishing or watching sporting events. The open pack photo comes from Wikipedia.
Even though places like Tokyo don't get particularly frigid in winter, plenty of people buy kairo, since many buildings still lack central heating. In particular, kairo are favorites of students because public school classrooms can be especially drafty.