What article is carried aboard the plane become an important symbol for survival in the novel, Wreckage?

Life vests are stored aboard the private jet plane utilized by Carlton Yogurt for its dream vacation contest getaways in the Fiji Islands. The life vests are meant to be used in an emergency should the plane go down over water. In the novel, the plane goes down in the ocean, and the life vests become essential to survival as Lillian and Dave must swim to the life raft with Margaret to push her on board.