The day before: Trim fat from meat. If necessary, cut meat to fit into a 3 1/2- to 5-quart slow cooker with a car adapter. Sprinkle meat with salt and pepper. In a large skillet cook meat in hot oil over medium-high heat until brown on all sides. Drain off fat. Transfer meat to cooker. Add onions, 1 cup root beer, and garlic. Cover and cook on low-heat setting for 8 to 10 hours or on high-heat setting for 4 to 5 hours.
Meanwhile, for sauce, in a medium saucepan combine 3 cups root beer and chili sauce. Bring to boiling; reduce heat. Simmer, covered, about 30 minutes or until mixture is reduced to 2 cups, stirring occasionally. If desired, stir in root beer concentrate and hot pepper sauce.
Remove meat from cooker. Using a slotted spoon, transfer onions to a large bowl and discard cooking liquid. Using two forks, pull meat apart into shreds. Add shredded meat and sauce to onions; stir gently to coat. Transfer meat mixture to a storage container; cover and chill overnight.
Tailgate day: Transfer meat mixture to a large saucepan. Reheat, covered, over medium-low heat for 10 to 15 minutes or until heated through, stirring occasionally. If necessary, add 2 to 4 tablespoons root beer to keep mixture from sticking. Return meat mixture to cooker.
Tightly cover slow cooker and tote in an insulated carrier.
At the tailgating site, plug slow cooker into car adapter if necessary and keep meat mixture warm on warm-heat setting.
To serve, fill with meat mixture and top with coleslaw. War Eagle.