How do you complete Grand Theft Auto without doing the missons?

Answer 1

well, you have to beat off the boat, but afterwards you can just get a weapon, then a stronger one, and stronger until you have an uzi, pistol, shotgun, bat/knife, and maybe even a grenade. then steal a cop car and do vigilante mission, once you max pistol ammo enemies will use the next tier until you maxed that all the way to assault rifles. gang activities help. then once your done with that, find some body armor and a good car, save, and their, your set to kill, and wreak havoc to all the place you have unlocked! it's possible, and I've done it!

Answer 2

There are some missions you can miss and go on to complete the game, for example, the Wang Motor missions and Zero's missions in GTA San Andreas, and the No. 1 mission with Brucie in GTA IV, but you would not get a 100% completion in the games, and also you could miss out on connecting missions and sub missions. Otherwise, you might be able to go down the cheat route. Might be worth browsing gtawiki for further information:

gta.wikia.com