West Yellowstone to Missoula Lunch Spot
What kind of food/experience are you looking for? Are you taking the fastest route, or do you have time for a side trip?
I can recommend a few places in Butte, whether you want to sample a classic cafe (or two), a greasy local delicacy, Cornish pasties, a good hamburger, local pizza, organic food, fine dining with daily lunch specials, or an Italian market with good soups and sandwiches. Unfortunately, a lot of the smaller towns don't have much to offer, but I can think of a few places worth visiting.