For the ODST outfit, the best soft parts to go with in my opinion would be EMS Black Pants, Underarmor long sleeve shirt, and Brahma SWAT Boots. There may be other alternatives to this if you have any suggestions please feel free to provide.
For the Halo Master Chief outfit, the best to go with for this would be a black Lycra or Polyester bodysuit, with a SixSixOne Chest Protector for mounting the Torso and Shoulder Armor to it.