Okay, I've had THREE kids and didn't discover till my third how easy it can be to travel with baby and bottles. I always stressed so badly over formula temperature when I'd try to go out with my first two. You just can't make a bottle 3 hours ahead of time and it be safe to give your baby. Pediatricians told me after mixed formula was good for ONE hour before it started building up harmful bacteria. So I'd try taking bottles in a cooler and heating them in those car warmers. THAT was an extreme headache. It takes those about 30 minutes to warm a bottle. Then I tried the powder formula and found I preferred it to the ready made or concentrated types. But my babies wanted formula warmed. TO MY ABSOLUTE RELIEF a friend gave me the idea of carrying a Stainless Steel thermos of warmed water and putting the formula powder in the bottles.  Sometimes things that seem like a no-brainer, are so out of reach when you have a baby that needs you to provide everything for them.  Also my thermos would keep very warm water warm for two days.  You don't have to overheat it thinking it'll cool down either. Just SLIGHTLY warmer than you'd serve it, and your good to go.  This was one helpful tip that made me not despise having to go out with my children. Maybe it'll take a bit of the stress out of your days with baby as well. :)