For this achievement you need to try every vehicle, every standard level and every character at least once.
There are 24 vehicles: Delivery Van, The Wedge, Maximus, Pink Lightning, Red Hot Engine, Mall Racer, Sasquatch, Smooth Cruiser, Corley, Ranger, Street Slicer, Komrade, Cool Streak, Boss Throne, Boogie Bus, Heavy Metal, The Swinger, Token Bird, Shuriken, Grim Wagon, Squealer, Wastelander, Ricky-tick and LeDorean.
There are 8 characters: Mr. Dismount, Ms. Dismount, Mr. Heft, Ms. Bumblebee, Mr. Reach, Mr. Stalwart, Ms. Diva and Mr. Ego.
There are 26 levels.
Totals are correct as of 1/11/2015.