My wife has been putting frozen plastic water bottles in my lunch box for years with no problems of leaking. <br><br> If one were to use some of those disposable hand warmer packets wrapped togeather with the frozen water bottle possably in a towel or water parka, it may melt the ice so the water is available to drink. <br><br> The type of hand warmer listed in Campmor claims average temperature of 135 deg. F. for up to 7 hours. Just a thought.<br><br>Neal