Zippo Rechargeable Hand Warmer  – Link

Amazon has this currently on sale for just $24.99.

• Rechargeable 5200 mah lithium-ion battery (included) for lasting reliable warmth – up to 6 hour Run time
• Dual sided heat up to 120 DegreeF/50 DegreeC operating temperature with five (5) heat settings for adjustable and comfortable warmth
• Battery and heat indicator lights
• Charges USB compatible devices including; mobile phones, Mp3 players, tablets, cameras, etc
• 1 year warranty