I'm playing gta v finished the game?

If you haven't got 100% then maybe go for that. Do the flying challenges, stunts and collectable things for example.

Why not try online? That can keep you going for ages ranking up, getting cars etc.

You can also replay missions too. Why not try to get gold on them or replay ones in a different way (heists usually have 2 methods so why not try the method you did not originally choose?

Or just simply explore and think of loads of stuff you could try, from diving to stunts, animal hunting (single player only) or whatever you fancy. There is loads to do if you put your mind to it.

Online's fun if you never played it yet or you could try to get 100% completion in the story mode.

Go outside

You can play other games may be baseball