I read about a weird type of hot pack years ago. Basically it is a special gel that is cool to the touch. You felx a simple little metal disc inside - it pops and the gel suddenly gets hot - to recharge you stick it in boiling water for 15 mins. You can leave it as long as you like - pop the disc and instant heat!!! It really is incredible to see - like black magic in action.
Never seen them on sale before - found them in my local Tesco - £1.97 for a pair just the right size to slip inside a glove or pocket. Could even save you from frostbite on the boat. Tried them straight out of the shop - they are already precharged.
another brilliant bargain was a £1 knife sharpener. It looks like a knuckle duster and has grooves for knives or scissors. I have had similar things before but this one actually worked - brilliantly.
These are similar - do all sorts of sizes - the bodywarmer etc could be great for treating people with hypothermia.