The idea with ice cubes is that you cook and freeze food in advance for use in cooking later or to simply warm up and offer as a main meal.
Vegetables (all sorts) are the easiest thing to cook and freeze in ice cube trays. Use your imagination on which vegetables to cook and just do the following.

Boil or steam the vegetables of your choice until tender. Depending on the vegetables you can blend or mash adding a little cooking water or milk if needed.
Allow for the vegetable puree to cool down then fill ice cube trays and freeze.

Once frozen you can move the ice cubes into polythene bags
(freezer bags which you can easily find in your supermarkets are ideal).
You can even write the content and the date on the bag:
the ice cubes will normally last 4-6 weeks.

TIP
if you have a calendar handy, check when the food expires and write the expiry date on the bag instead, it will be easier to spot what's still good and what needs binning.

 
It's easy, just use a microwave for a few minutes (stir well and make sure the food is evenly warm), or use a food warmer (it takes longer so allow plenty of time) or place in a little saucepan and stir until warm.
 

You can mix and match ice cubes for a meal
(ie 1 broccoli ice cube + 1 coliflower ice cube)

You can add cheese and/or milk to make it into a creamy soup
(cream/milk + 1 carrot cube)

You can also freeze most of the actual recipes on this website
so if you cook more than just one portion you will be able to offer your baby a varied meal in a few weeks time by just selecting a few ice cubes from your freezer when needed (depending on baby's age and appetite).


When your baby is around 8-9 months you will find it more practical to freeze portions in bigger containers.
You can use yogurth pots, glass babyfood jars, small margarine tubs, etc.
Breast milk freezer bags also do the trick (thanks Shenelle for the suggestion!)
I personally like to use fresh cream pots becuase they come with a lid, but if you don't have a lid, use foil to cover the container.