-Turn the auto shotgun into a something similar to the shredder from T2 (refer the the shredder mod).
-Possibly add a MAG60 3 round burst pistol with it's own skin.
-Giving the AR hollow point rounds as it's primary instead of pistol bullets.
-Adding a flamethrower.
-Either reworking, or replacing the alien gun with something better.
-Making hand grenades have a weapon slot where they can be thrown.
-Adding a flechette gun that can be used underwater.