How can you store formula feeds for going out and about?

I Am so confused on how to store formula feeds for when you go out. I have been told that you boil the water and can keep it in a flask which will keep it at the right temp seperate from the powder and then just mix it up when needed. I have milk powder despensers which i can store the milk in inside the bottle that has the boiled water in and also have thermo bags which i can put the bottle in to keep the right temp but what i was wondering is they say that the water needs to be at 70*C to mix the milk to sterilise it but what happens if you are out and you mix it up at that temp when the feed is need and its too hot still and you have no where to cool it down? Does the water have to be at that temp or can it be left in the thermo bag a bit cooler but still warm and then mix it so my baby can have it straigh away without cooling?