It would be nice to know the terrain/environment/general area, a description of the hunter, and what game you are hunting, the month that you are hunting in, and the duration of the hunt in hours, and the type of hunt - tree stand, stalk, duck blind, ground blind, dog driving, etc.

On your follow-up question about how do you get hunter's to carry a backpack - that's easy. You put things in there that they will use whether there is an emergency or not. If your pack only has emergency items, people will tend to stop using it.