Montana is a rather big state - it has about 100,000 more square miles of land mass than PA does. So, a specific answer to your question could depend in part on what part of MT you intend to visit, where you intend to fish, etc.
In general, however, the suggestions you’ve received so far are all good ones though. I would add insect repellant, a good raincoat, and some warm clothing to your list of items that you don’t want to leave home without. Like bear spray, you hope you won’t need to use them but they can be life savers if and when they are needed.