Probly too late but for fun:
Guns Jamming, different scopes available for purchase for the sniper rifle, cops will go after other peaple when they shoot you.
Being able to carry a silenced pistol, and a desert eagle, make the planes a little tougher, get rid of the 250k when you enter the health & armor cheat.
Sabre Turbo, an R.V that has a save in it so you can move it where ever you want.
More handguns, dynomite, timed bombs where you can set the Detonation time.
5 or 10% less money for missions, spike strips, being able to purchase bullet proof cars for a hefty amount of money.
Rivers that actully have a current, character limps when he falls running/walking speed is reduced.
more vocabulary for peaple, you see the empty bullet cases on the ground and they dont disapear in 5 seconds,
Also an in car view where you see through the windshield, not some bumper cam.