This quest is initiated by finding the bike first and beginning with Case 0-3.
The first part you collect, if you follow the story, is the bike forks.
Head to the alley behind the hotel, climb the dumpster and jump onto the semi-descended fire escape. The key is in the last room on the right. Collect the key, head to the shed next to the hardware store and open it to find the bike forks. Take the bike forks and return the to bike to collect this achievement.
You can also just head out to the gas pumps and collect the gas can. That one is easy enough to get.