Use your iPhone to slim down your wallet →
https://marco.org/2008/05/13/use-your-iphone-to-slim-down-your-wallet
This description by tgumbel is better than the article:
As if buying an iPhone doesn’t slim down your wallet enough.
It’s about a guy who puts scans of his grocery-store loyalty cards on his iPhone. Clever idea, but I don’t think it’s worth the trouble and the looks you’ll get.