I totally recommend putting your products in a plastic bag, especially since you're going to be going to widely different altitudes. Bottles could explode and get your clothes all gucky. I have had this happen to me soooo many times when going from Utah to California or Washington.
I also highly recommend taking a richer conditioner because Montana is bitterly cold and dry (according to my friend who lives there), it's going to be a little better now that it's getting to be spring, but even this time of the year it's going to be cold and dry. And it is a very arid environment overall. So I really don't recommend taking anything that has high humectant properties. And yes, I recommend something that has a higher hold property.
And I also do second whoever said that there are always stores up there where you can buy whatever you may have missed, or may have figured out you needed. I know there are portions of Montana that are super-remote and it actually is a little difficult to get to markets that might have the selection of what you need (trust me, I used to live in one here...but I was only 45 minutes away from the city, so it wasn't so bad), but hopefully you won't be in one of those places!
Planning on taking a bit of something for a DT might be helpful if your hair tends to be dry might not be out of the realms of possibility. It really is going to be dry compared to Alabama (as well as a rich lotion, too).
Sorry, I'm probably adding to and not removing from the list. I can take myself on roadtrips for about the same amount of time and do it with travel-size stuff. The only thing I might bring of full-size (simply because I have so much hair) is conditioner and maybe
Makeup, however, is my problem. I like to mix it up so much I have panic attacks when I whittle down my makeup to take on road trips to go see family or with friends to go to Vegas and clubbing or whatever...I probably need counseling.