Is a business card necessary for a graduate student? I know some PhD students have their own business cards, but I don't know if it is a standard practice for PhD students to have their own business cards. I think a business card can be useful for networking in conference or collaborating with some industrial partners. So, is are business cards necessary for a PhD student or other graduate students attending conferences? 

PS: in case it is field-specific, I would like to know the different practices in different fields
As a PhD student, I had business cards and never used them. Now I don't even have cards. I consider them a relict from different times. I would say nobody strictly needs a business card anymore, and I rarely see them being exchanged at conferences either.

Now, a homepage is a different story. You definitely need a homepage, for many of the reasons you think you may need a business card.