Get into a vehicle and head to the left-hand corner of the playable map. Maneuver your vehicle to about a meter away from the demo wall, with the driver side of the vehicle parallel with the wall. Rapidly press Y(2) for your player to jump from the car and jump through the wall. If you are not sure of your position, press Start and make sure a green circle with a question mark is nearby. Walk to the store (or the green circle) and open the front or back door to find a drug store.