For most locations, they are already setup for paperless receipts.. unfortunately you have to ask them for a digital receipt.. Walgreens does it, CVS, etc. It SHOULD be the other way around and ask if you want a paper receipt!
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Don't quote me on this, but I don't think PayPal will be around much longer. PayPal was invented to move to a paperless society before the push on NFC. Now that EBay has DROPPED PayPal completely as a separate company, if they go south really quickly.. They can separate themselves from that easier - or use both PayPal and ApplePay without a major conflict of business interests.
Look at the major retailers that AREN'T supporting ApplePay right now.. hmm.. most of them take PayPal!! HomeDepot, Wal-Mart.. etc.
The real question is, with the volume of business that Wal-Mart gets.. how long before they drop PayPal for ApplePay? Not long!