I do same as above...it's so much easier when you are out as you don't have to take hot water to heat the bottle or find somewhere to heat it. Bubs doesn't get used to it always being heated either. Also when you go out if you cant keep it in the fridge it's not good after a couple hours. So easier to make up as you need them. I wash all my bottles, boil the water, fill them all up & pop them in the pantry...then they are ready to go when needed, just have to be mixed. Also if you use a thickened formula it's not recommended to leave it as it thickens up as it stands.....so best to prepare just as needed.