Fine. You don't have to be on it for long. Get off at the first exit west of Rock Creek Rd. and then follow the parallel roads to the north of I-90. IIRC, there is even some bike trail/rideable sidwalk. Keep goingf past the post office and golf course and then you will evetually cross under I-90 and end up on E. Broadway. This is basically what we did to ACA's headquarters:http://ridewithgps.com/routes/6669195
Rock Creek Rd. is a wonderful ride. Did it from the Jct. with MT 348 in 2011. If you want a commercial campground, there is a nice one right by the creek just before you reach I-90. No groceries near, but the restaurant is good.http://ekstromstagestation.com/
I think we stayed in site No. 14.
Maybe 10 miles before you get there, you will pass Trout Bum, which is an outiftter and real estate agency. They have good coffee (including espresso). They also sell energy bars if you need a snack.
Just a bit of a warning: I see you plan to ride Skalkaho. This past June I rode the entire length, from MT 1 to Hamilton. Up from Hamilton, it's a long slog, and once you hit the dirt it can get steep, bumpy and rocky in places. The descent down to Rock Creek Rd. is a nicer surface and is actually paved for a decent stretch in the middle. Dirt ends just before Gem Mountain.
The Gem Mountain c-store shown on your map had very limited snacks and drinks, including bottled water (no drinkable tap water), and a few nukeable sandwiches. It's not really a store per se. They just sell stuff out of the office. If you have an hour or so to kill, I recommend buying a bucket of dirt and panning for sapphires. Make sure you have bug spray.
Once you turn left onto Rock Creek Rd., you will pass The Ranch at Rock Creek, which is an exclusive, all-inclusive resort where cabins go for over $5K/night. Doesn't seem like the place to pop in for a snack. Trout Bum, mentioned above, will be the next source for snacks. I think or more of the campgrounds shown on your map have water.
There is a really seedy bar at the I-90 interchange which is home to the "Testicle Festival." If they serve food, they were no longer serving it when we walked there for some take-out beer. Even if they had been serving food, I would have only eaten there if I had been starving. Treat yourself to a steak and salad bar if you stay at Ekstroms Stage. It's going to be a long day if you come from Hamilton.