communication system
All children need a communication system in order communication to obtain sense to them. It doesn't matter if you use pictures, objects or gestures, as long as the child understands the meaning of it.
The problem often occurs that the behaviour of autisc children is rather coincidental. That means that they don't have a real preference for anything, but instead occupy themselves with whatever they find on their way. It is not easy to learn a communication system then, because they have no incentive. In order to learn the procedure of communication, they must want something enough to make an effort to get it!
Here food can be of help. Usually they like a bite of something every now and then.
Playing with your child will eventually give him more incentives to ask for. Just be patient and it will surely happen. Then is the time to obtain a communication system which will be learned in no time.