How do you combo bikes in Dead Rising 2

In order to combine things with the bike in Dead Rising 2, you must complete the "Meet the Contestants" mission, in which you must defeat Leon. After you defeat him, go back to his bike trailer with one of the following items

• LMG
• Giant Stuffed Rabbit
• Chainsaw
• Rocket Launcher (Combination of Lead Pipe and Rocket Fireworks)

Combine them with his bike, and you will have a combo bike!