Police might be a bit suspicious if you offer just one card, but a range of cards, work security pass etc would do it. I'm not taking a passport or a driving licence.
Then again, like 99% of fans, I'm not going to do anything which will prompt police to ask for ID...
Is this still news? A load of bedwetters getting in a fuss over nothing.
No-one has specified passport or driving licence have they? A credit card will do - in the highly unlikely event that you get stopped. Ooooh, my poor civil rights!