Garrett in Montana? Good deal. I may be a day late and a buck short, but here goes...
Make it down to West Yellowstone during the week. You picked a rather crap time to go, most of the locals are about ready to head back to school. So, everyone is usually getting their last run through the park in about now. Get your day permit and go fish the Firehole river. A bit tough getting to as you have to mind your step through the steam pots, etc., but well worth it. The fish aren't trophy class, but they fight like fish 5x their size. Get there early, the fishing is good...and popular. Besides, there are very few places on this earth where you can land a trout within 100 yards of a herd of Bison. Truly epic.
If you got some more time, head out the South Entrance from Yellowstone and head through Teton National Park. Absolutely incredible drive, with plenty of wildlife sightings and enough views of Grand Teton to make your shutter smoke. Make it down into Jackson Hole, pony up at the Million Dollar Cowboy Bar for a drink, and leave before you decide to eat (the food sucks and is way overpriced). Head on over to Jackson Hole Brewing Co. about 250 yards away and enjoy some great brews, laid back atmosphere, and much better food. If you're feeling touristy, make sure you get your pic taken under the antler arch.
And, if you're really in the mood for a drive, head East out of Jackson to Idaho Falls. Give me a ring and I'll show you around. First beer is on me.