Best bar to meet diverse people and get wasted (good cajun food too): Charlie B's
http://www.yelp.com/biz/charlies-bar-missoulaBig Sky Concert series: yes, saw Wilco there last summer. Another good concert series is the annual Roots Fest (august?), where they close off downtown streets, bring in good acts for the outdoor stages, food trucks, beers, good times. An everyday kind of good local music venue is the Top Hat.
Kelly Creek: Yes! A favorite! Stupid good cutthroat trout fly fishing. If you go, hike upstream from the end of the road to fish. Not that close though-two hours away at least. Some other good camping and fishing options are closer, like Rock Creek.
Lolo creek/pass: nice drive, a couple of decent natl forest campgrounds, and a good hot springs place at the top, great place to get in a shower and soak if you've been camping and feeling all grimy and stuff. Also, if you go on over the pass the Lochsa river beautiful and decent fishing for smaller cutties and has cool rope bridges and a trail to a remote hot springs where people get nekkid (Jerry Johnson Hot Springs.)