Go to an explosive mine field and jump head first.
Hide myself inside the missile shell of a fighter jet, that way, when the missile fires I'm in it and able to steer that shit. Right before it explodes I would jump out and hit the nearest soldier with a drop kick. The velocity would be so high that we would both Disintegrate on impact, leaving a splatter of blood where he stood.
Go inside the nuclear load of an ICBM until I get enough radiation built up in order to grow 100 feet tall and be able to kick tanks and punch planes out of the air. The enemy army would need to get their very own 100 feet tall radioactive soldier and we would battle it out until one of us dies...
Build myself a suit out of stainless steel and go up to the international space station. I would drop from that height straight in the middle of united kingdom, that would sink the island...
I would fuse my DNA with a bears, making forest combat possible. Then I would go into the woods without the enemy noticing (thinking im a full bear). I Would then climb the trees and wait for enemy soldiers to pass by and maul them with my bear strength. I would then unfuse my DNA because I obviously do not want to be a bear my whole life...
Become the glitch (like wreck it ralph) and then go into the enemies communication systems and switch the language of all their shit to chinese, leaving them incapable of communicating properly and giving us a W in the war. I would then switch my own teams language because why not? There would be peace on earth because no one would be able to use their high tech shit.