One of the items originally offered as "extras" were carrying/storage bags. These bags were well made and insulated. They are not as common to find as sets themselves, even though later on they included them with every pot. However, these bags are still around. And they were much more useful than was originally labeled because they allowed cooking times to be extended a great deal. In short it was easier to cook with them then without especially in the winter when a house was cooler than in the summer as the pots will hold the heat for a longer period. But you can easily make your own or just use several towels/fabrics wrapped around them to help the pot hold heat longer. Of course a quilted bag will work better and here is one design:
http://www.twentymile.com/Cookbook/aircorecozy.htm
If you have a design of your own, do let us know. The person above also had a idea of using the Pyrex Microcore® Heat Packs to extend the cooking time (and time of the meal staying warm) even longer. I have heard some people say that they didn't have good results without the carriers. However, we didn't have a problem without them. Anyway they are a good idea (especially if you have problems with a meal cooling too soon) and it is easy to make your own should you not have the original carriers available.
Another tip...DON'T PEEK! Every time you lift the lid (even just the ThemroKnob outer lid) you loose a lot of heat. And since AirCore depends on trapped heat you may remove enough heat that the meal fails to cook properly. If you are experimenting and absolutely have to to peek, I would suggest heating the pot on the stove for a few minutes to compensate for the heat you lost. In short.. DON'T PEEK. I am sure you have heard of the saying "a watched pot never boils" well in this case "a watched AirCore never cooks". The whole idea of the system is you just heat it up and walk away without having to do anything more. On the good side, you can always add more heat if need be (unless you are out traveling or are taking dinner somewhere else (say a picnic) then this could be more problematic. ;)