The special pre-order items vary depending on the retailer you purchased Just Cause 2 from.  The pre-order packages are listed below.

WalMart - Agency Hovercraft
Best Buy - Chevalier Classic Car
Amazon - Bull's Eye Assault Rifle
Gamestop - Rico's Signature Hand Gun and Monter Truck
Target - Chaos Parachute

For more information regarding the pre-order special item please visit the Just Cause 2 Official website at http://www.justcause.com/us_pre-order