I got the idea for this costume literally a night before Fanime 2007. *Warning: I'm about to say a lot of shit that most people probably won't care about. It's how I made my costume*
I had all of the equipment I needed for the costume, which was a lot of Vietnam era gear that I used for reenacting (I am a Vietnam reenactor). The fatigues I wear are the Type 3 Jungle Fatigue uniform in olive drab or ERDL camouflage pattern ("Leaf" camo in the game). I wear some offbrand underarmor-type form fitting shirt underneath and a neoprene kneebrace.
The gear belt I used was the USMC M61 pistol belt, which is basically your generic pistol belt, with two M56 pouches on the left side of the belt, an M67 buttpack on the rear. On the right side I have the standard black leather US M1916 hip holster with my 1911 in there. Right behind that is an M67 magazine pouch for the M14 rifle, which I use for a radio pouch.
The harness is what's keeping this costume from being 100% complete. Snake used a STABO harness, which I plan on making out of an old parachute harness (when I make it, full credit goes out to TheOrange for his tutorial on how to make the STABO). The radio I have is a block of wood sprayed black with some nuts and bolts glued on. I jerry rigged a throat mic out of some old headphone earpads fixed to an elastic strap that I put around my throat (obviously..) with the headphone cords hot glued on there. The headband is just an olive drab strip of cloth. I made the knife out of a thin sheet of plexiglass. I cut out the knife pattern, gave it some contour and shape with a round file, and sprayed it silver. I wrapped the handle is OD paracord as well, just like Snake's. The sheath is also still being made. The boots I wear are just Vietnam era jungle boots that I picked up from a surplus store for $25 (they're the most ungodly painful thing to wear. Goddamn cardboard inserts). The survival knife is just some rubber dagger with white fabric tape taped around the handle in a leather ka-bar sheath duct taped to my leg (using OD tape).

This costume has basically become my favorite costume ever. I mean, who's cooler than Big Boss? No one, that's who. He's a man so undoubtedly awesome that he cloned himself just so he could kick his own ass. ahaha.