Ah OK. Your English is good.
2 match heads would be ok. If you could get some smaller as he is a bit s,all that would be ideal. He can choose what he needs. As royal chick says next time you are out and about just pick up gravel/dirt from anywhere. Put it in your pocket, give it a wash and let him have it.
You only need to soak enough food that he will eat in one day. It only takes a few minutes to soak it. So it's no trouble to do it each day. You could even mix the wheat and corn into it to encourage him to eat it.
If you have a pair of pliers and little bit too large grit, you can easily make it smaller without smashing tiles inside the house by crushing it.