Equip a box in the various game areas to travel to the destination on the boxes and easily skip areas. The boxes are located as follows:
-In Tank Hangar level 1, on the top floor, in the room by the stairs. In the Arms Storage building basement 1, in one of the rooms inside the main room on that floor.
-In one of the storage rooms in the courtyard where the second confrontation with Sniper Wolf took place.
To use the boxes (A, B, or C), jump in the back of one of the trucks located in each area and hide in the box. Eventually a soldier will notice and drive Snake to the destination labeled on the box:
-The Heliport -The Arms Storage Building -The Field (where Sniper Wolf was killed)
This trick can be used to save time traveling between buildings, and also keeps Snake from being in the cold for extended periods of time (preventing the sneezing and sniffles that alert the guards to his presence).