What does your wife want in the bag?

If she cares, explain what all you are considering to put in it, what is in yours, and when the bag would be used. Then ask her which items she wants in her bag.

If she doesn't care, make it as easy to use as possible, and don't expect her to reach for it until you are in the middle of an emergency and you tell her to grab it.

My main piece of advice is don't expect your wife to actively carry anything that she thinks is pointless. So, trim stuff that she objects to or gently educate her on its usefulness.

-Kuovonne