In trying to live a relatively paperless lifestyle, I notice what options stores and restaurants offer for providing electronic receipts instead of paper ones.
My favorite kind is where you use a credit card or mobile payment method that some lower level of infrastructure already knows about and you automatically get an email receipt without further prompting. Square has a great implementation of this.
Slightly less awesome but still great is the version where you use a digital payment method and then have to enter your email address manually, even if you've used the same payment and receipt delivery method at the same location before (I'm looking at you, most American chain restaurants that have the little mini-computer waiting at the booth when people sit down). A bit annoying, but still paperless.
Then there's everywhere else where printing a receipt is probably the only option. Especially at the grocery store, where the receipt and personalized coupons are several miles long, requiring their own bag to carry out. And look, there I am a few days later, awkwardly holding a crumpled piece of paper up next to the networked super-computer on my desk, manually typing in some details that some other networked computer somewhere else already knows about.