And people say no question is a dumb question...torontowii said:do you NEED a blockbuster card to rent a game?
Cards hold your personal info so that they may contact you in case you lose/ owe late-fees and so that they have an address to send the police to once you don't return it.
You don't need a card to buy products though, personally, I wouldn't dare buying from Blockbuster because their discs are in such bad condition half the time from lying around at 10, 000 different homes.