How does Jack wish to contribute to the survival of the boys?

They will be responsible for hunting and finding meat. The are also the defacto "army" on the island lead by, of course, Jack.

Jack wishes to be the leader of a hunting party on the island. He explains that, this way, there will be a source of meat in the boy's diets. However, I think that what Jack really wants is to make up for his failure of being able to kill a pig in the beginning of the book. Furthermore, by killing and hunting, Jack thinks that this is a source of power. To him, power is violence so he thinks that his being able to hunt will prove that he should be the leader instead of Ralph. As you can see, Jack seems to care only about power rather than the well-being of the boys.