Dawn,
I've been following along as best I could with as many irons as I have in numerous fires at this time. A handful of quick and fairly easy ideas follow:
Eats and drinks: At the junction of I-90 and US-287 just west of Bozeman, MT is "Wheat, Montana", a production and retail complex which produces, sells, and bakes with a seemingly infinite variety of flours grown right there on a large family farm. Superb breads and pastries, excellent sammiches, great coffee, and very nice folks. Around 75 miles southwest of there in the county seat of Beaverhead County, Dillon, is La Fiesta Mexicana, more widely known as the Dillon Taco Bus. Home-cooked and head and shoulders above any Mexican food I've ever had anywhere, right down to the cane sugar Mexican soft drinks. Along the "Montana Scenic Route", MT-1, which loops from I-90 at Anaconda back to it around 35 miles east of Missoula is Philipsburg. P'burg is as nice of a town as you'll find and if you like that kind of thing the Philipsburg Brewing Co right on Broadway makes several very good varieties of beer. Other taverns and cafes serve good meals.
Driving routes and hot springs: MT highways 55 and 41 will take you from I-90 just west of Wheat, Montana (above) down to Dillon and that's a very nice drive. Along the way you'll pass by Beaverhead Rock, a location of significance to the Lewis & Clark outward trek, which you'll be following from Twin Bridges to Dillon. If you get on a L&C kick, take I-15 on south of Dillon for around 25 miles to Clark Canyon Reservoir, then MT-324 west to the well-marked turn-off to Lemhi Pass, where L&C first crossed the Divide in August 1805. At the pass, two roads descend to ID-28 just south of Salmon--Agency Creek Road is steep and I've never driven it. Warm Springs Road follows the Divide a few miles north before descending and passes by Sharkey's Hot Spring near ID-28. Sharkey's is a BLM facility which has been developed by construction of two nice concrete and tile pools, concrete aprons, changing rooms and bathrooms, fencing, and a graveled parking lot. During the week you may be the only person there. It's in the full sunlight all day so a hot sunny summer day isn't the best one to visit, but a cloudy or even a rainy summer day would be splendid. If you were to do this long loop over Lemhi Pass and back to I-90 at Missoula via US-93 from Salmon, your truck is a cinch to handle Lemhi Pass and the Warm Springs Road descent on the ID side. Just be sure to fill up on fuel in Dillon at Rocky Mountain Supply ( conveniently just up the street from the Taco Bus) before heading down I-15, as there is no fuel or services from there to Salmon, ID, and that's around 100 miles distant.I think you saw a discussion including Horse Creek Hot Spring over on the far (western) side of US-93 north of Salmon, ID in my "Montana Trip Planning" thread and I'm still keen on getting over there, though probably not on the September trip. And if you were to just loop through Philipsburg for a day or two while generally westbound on I-90, consider the easy drive through Rock Creek canyon as a route back to I-90. MT-348 leaves P'burg to the west and connects to Rock Creek Rd (FS 102) at the Bohansen Memorial Bridge on Rock Creek. From there it's 41 miles north to I-90 and only the last 10 are developed (and paved). Rock Creek is a "blue ribbon" trout stream with a half-dozen NF campgrounds and a goodly number of designated streamside disbursed sites. With a leisurely late morning start from P'burg, you could spend 4-5 hours driving down Rock Creek and would reach I-90 about 20 miles east of Missoula in the mid-afternoon.
Missoula: Home to the University of Montana, and due to its relatively low elevation being referred to as the Garden City, Missoula offers a wide range of walking tours of coffee shops, cafes, restaurants, and bars. There's a large Costco and an Academy Sports for resupply needs, too. We love Missoula.
Enjoy your Wandering!
Foy