I would prefer one card, one that has embedded into it:
Your drivers license
Your credit cards
Your industry licenses
Your Medicare card
Your Flybuys card
Your myki card
etc etc etc
Easy to do with technology now and readers can be set up to just read the portion of the card relevant to what card aspects they need...but then the Wallet manufacturing companies would go broke, cows and pigs wouldn't be needed as much, price of meat would drop, heck...why don't we just all have a chip inserted under the skin with all our info from our cards plus GPS location, pacemaker ability, cochlear capability, etc etc etc...you get the idea, would be good though
(Now, where is my wife at the moment.....stuff the wife, WHERE IS MY 17 YEAR OLD DAUGHTER RIGHT NOW)