duct tape can do anything.
I always bring duct tape. It can do anything. Make arrow flights, temporarily patch up blisters, help tie a raft ( or shelter), fix clothing and shoes. Obviously this is not the most important thing (it is not more important than a knife or flint) but it might be the most versitile thing you can carry. I usually re-roll the tape on a ball point pen or pencil to make it more compact to carry. If you bring your wife along ( my wife will occasionally make it on a camping trip or two), it can also be used as a noise reducer if you place it correctly across her lips ; ).