A pair of denim "overhalls" would be good.
Foxworthy's Redneck Dictionary would be excellent.
Rebel flag hat, bumper sticker, or window decal (especially if the DU, Browning Buck Mark, or similar logo in "Rebel"). If you can find it, the one that says, "Clean Up the South, Buy a Yankee a Bus Ticket Home" is always good.
A copy of "Deliverance" would be classic - thank the Lord Burt Reynolds kilt someone dead, or it'd just be a love story/chick flick. Nothing tugs at my heart strings like that "Dueling Banjos" serenade.
Get him a pair of jeans - and if you can get the Skoal ring in the back pocket, so much the better, but that's hard to fake.
A mullet wig, black velvet Elvis painting or some Graceland souvenir, NASCAR (preferably Dale or Junior) hat, shirt, jacket, commemorative plate (must be displayed in the house).
Corn cobs - make sure you get reds and whites.
Lynyrd Skynyrd - pretty much anything.
Tell him not to talk about hockey or ice fishing for the first six months at least. Football and basketball. And that y'all is singular or plural, all y'all is plural, and you'uns or y'uns is y'all plus 3.
This could be one hell of a Southern Transition Kit. Oh, and don't say "Civil War". It's just "The War" or "The War of Northern Aggression".