Oh sorry Lou - I didn't see your post before I went out!
I used to take a pre-made and heat them up. If I knew she wouldn't want it for more than 2hrs I would pop them in a cool bag with an ice pack and it would last for about 6hrs xx
If I knew she would want one pretty much as soon as we got there or within an hour I would heat one up before we left, and give it an extra few seconds, then it was perfect temp by the time we needed it xx