I seriously hope that we will have more and more diverse guns in GTA V and specially with much better sounds (GTA IV weapons didn't sound very good also had no echo). I am still waiting for the game that does justice to the real noise guns produce, guns completely muffle any other sound around, be it voices, cars, anything, so we should hear loud blasts and echo. The best weapons in GTA IV was in TLAD, the Automatic Pistol!
I also hope there will be individual snacks, liquor bottles, packs of cigarettes and more restaurants, those kind of details are the difference between games and GAMES. Getting ice creams, drinking coffee and donuts, having some kebabs, pizzas, pastas, sushi et cetera would give the game more immersion and more life to the map.