Now with it being said that you can change uniforms why couldn't that include a selection tactical vests. Each vest holding a different number of mags and gernades. I was able to stuff 14 5.56 clips, and a few 9mm clips in the vest I used. Then you have some straps to hang gernades. As an option you have a backpack were you can stuff with everything else.
This is were weight would come into effect. And to add to "OH MY LEGS ARE TIRED I WALK NOW" I agree with you. It would be cool if adrenaline was put into effect. Not like other games were time slows down but when you are being shot at you have the ability to run till you pass out.
These are just a few ideas that may or may not work out. Let me know what you think.