Does she know about this bag? If so, get her input. If it's a surprise, leave room in it for what she thinks is important.

Is this going to be in her car, sort of a Bug-Home kit?

Whichever, it needs to cover at least the basics: shelter, warmth, water, a way to signal for help, and food (food isn't a real necessity, but it can help comfort, and help keep your body heat up).

I would put enough stuff in her kit so you could both use it, in case your kit gets stolen, lost, burned or buried. Keep a copy of important phone numbers, policy numbers, etc in both kits, waterproofed.

Sue