How can I make my hair grow perfect straight without straightening products and stuffs like that?

Your hair is programmed to be curly -- just like mine will never be curly. I used to hate my stick-straight hair, and my sister hated her curly hair. You get what you get. Straight hair can be permed or gelled/curled, but it will always go back to being straight. Curly hair can be straightened, but once that stops, the hair will be curly again. No foods or pills will change that. My sister and I have learned to live with what we have and find hair styles that look good. That's what you need to do too.

You can't. The way your hair grows is part of your genes. You can no more make your hair grow straight than a man that's balding can grow hair. It is what it is.