First, I'm not a lawyer, so no legal advice here, etc. Second, it's been a while since I bothered to research this stuff. That said...
In TN state law allows an open container, but there are muni laws which prohibit it. So in downtown Nashville it might be illegal but on the interstate it may be legal. In college we always just roadtripped it with a cooler full of beer, but were never pulled over. I've also had little trouble with cabbies letting me in with an open, but again, ymmv. Finally, after being the sober driver for a couple buddies flasking their way through Disneyworld, nothing is more aggravating than some drunks partying in the car while you're trying to watch the road.
Memphis is very thin for craft beer. Ghost River is a local, and High Cotton is a new startup - not sure how available they are. Nashville is better, with Yazoo, Jackalope, Turtle Anarchy, and Fat Bottom all in city limits, along with brewpubs Blackstone and Bosco's. Depending on when you're coming through, three of those four may be closed to the public, as they have more-or-less weekend hours, so check online for sure. My favorite beer bar in Nashville is 12th South Taproom: wide selection, but not so big you'll get a beer that's been in the lines for a month, knowledgeable staff, good food. There's a Flying Saucer downtown that has a big selection as well.
