I did the same thing Jane C does. The ones on one step ahead are a little small so if your baby has a big appetite, you can go through those containers quickly and have to refill and freeze often. Just put pureed food in an ice cube tray, freeze, pop it out and place in a zip lock bag. I made all kinds of combinations this way, too. I would put a cube of butternut squash and a cube of cauliflower together once the baby's palette became more developed. A cube of peas and a cube of carrots, a cube of broccoli and a cube of potatoes, etc. After a bit, I would introduce a cube of turkey or chicken into the mix.
For the convenience of a baby food jar, I used Gladware mini rounds. Puree the baby food, put them in there and freeze. When you on an outing, take one out of the freezer and use it to cool the other items in the bag and after a few hours, the food is fully defrosted and ready to eat!