well since you can't microwave baby food, there isn't another better way than to get a half cup of hot water that you can place the jar into.
We often carried a small thermos for warming, since our DS wouldn't eat baby food cold either. It works great. Just fill the thermos half full of boiling water. It will stay hot until you return to your resort for nap time.
Bring an empty thermos to the airplane if you are flying, and the flight attendants will fill it half way for you....works great!
Have a great time!