Checkpoint A. You will enter a room which requires you to turn a gas valve. 
  Ignore the valve, and instead go to the middle of that corridor. You will see 
  the Mirror's Edge logo next to an area where you can Wall Jump up to. Wall 
  Jump on the wall with the logo. You will find a bag as you climb up.
  Checkpoint C. Immediately after Miller tells you to go to the roof, turn to 
  your right, and run past the stairs. Use the red chair on the left to vault up 
  to the platform with a bag.
  Checkpoint D. Exit the elevator, and jump across to reach an area lit by 
  orange lights. Enter the vent after the first area. Drop down from the vent, 
  and find the Mirror's Edge logo. Wall Jump up above the logo to reach the bag.