Amazon has the 60-Count IRIS USA Large Disposable Hand Warmers on sale for $20 - 15% off coupon (check "Save an extra" box, eligible on first S&S order for this product) = $17 with free shipping on $35+ or with Prime (extra 5% off with 5+ S&S orders).

• Lasts up to 18 hours / Max Temp: 165°F / Average Temp: 142°F
• Do not place the warmer directly on your skin.