This isn't a full list of tracks, karts and items in the game. This is simply what has been unveiled thus far, compiled into a single list.

Mushroom: Toad Circuit, Daisy Hills, Cheep Cheep Lagoon, Shy Guy Bazaar

Flower: Wuhu Loop, Mario Circuit, Music Park, Rock Rock Mountain

Shell: N64 Luigi Raceway, GBA Bowser Castle 1, Wii Mushroom Gorge, DS Luigi's Mansion

Banana: N64 Koopa Beach, SNES Mario Circuit 2, Wii Coconut Mall, DS Waluigi Pinball

Other Cups: Star, Special, Leaf, Lightning

Battle Stages: GBA Battle Course 1, N64 Big Doughnut, DS Palm Shore, Honeybee House, Sherbet Rink, Wuhu Town

Drivers: Metal Mario, Lakitu, Mario, Luigi, Peach, Yoshi, Bowser, Donkey Kong, Toad, Koopa, Daisy, Wario, Rosalina, ShyGuy, Mii, and two more

Items: Super Leaf, Fire Flower, Lucky 7, Mushroom, Triple Mushroom, Golden Mushroom, Green Shell, Triple Green Shell, Red Shell, Triple Red Shell, Blue Shell, Banana, Triple Banana, Blooper, Bullet Bill, Lightning, Super Star, Bob-Omb

Karts: Birthday Girl, Bruiser, Blue Seven, Bolt Buggy, Standard, Cact-X, B-Dash, Yoshi Egg, Bullet Duck, H2O, Banana Buggy, unknown Bee-shaped kart

Wheels: Standard, Slick, Roller, Monster, Mushroom, Wood, Spongy

Gliders: Flower Glider, Peach Parasol, Super Glider, Swooper, Parafoil

Modes: Grand Prix, Time Trial, Balloon Battle, Coin Runners

Impressions here
Link