Continuity mistake: When Michael gets on the at the transit station, the camera pans down the bus aisle. The thief is not in the scene. The camera pans back to Michael then back down the aisle. The thief is now sitting in his seat.
Continuity mistake: When Michael is being chased by the agents, he goes through the transit station and hops on a bus. The camera shows the bus aisle. There is no street kid in the bus seat. When they pan back to Michael and then down the aisle again, the street kid is in his seat. A few other passengers have changed also. (00:35:15)
Other mistake: When they look at the winning lottery ticket that is hidden under the bird cage the lottery numbers are in the same order they were on the TV but when you buy a ticket the numbers you pick are printed in ascending order, not the random order that they would appear when they appear on live TV. (01:53:30)
Answer: He could have got someone to obtain the key and bring it to him. The same goes for much of the other stuff in the envelope.
Xofer