Power
You have the power to pedal—long, hard, and fast.
You'll develop super powers of intuition and a great sense of direction. You could be winning bike races and marathons, but instead you chose to deliver important legal documents that might make or break companies. You might deliver forgotten keys, congratulatory bottles of champagne, a director's reel, an actor's sides, or a much-needed pair of glasses.
You could be carrying precious jewels, loaner diamonds, or engagement rings from Cartier. How fancy.
Beyond what you carry, though, you're pretty low on the food chain. You won't be telling anyone else what to do in this line of work.