Some of the interesting newer apps I'm seeing are pay by phone mobile pay systems..Google Wallet, Square, etc..I haven't tried it yet, but a buddy of mine can preorder and pay by phone as we walk from the office to the neighborhood ramen shop, and then walk up to the counter and show the cashier the receipt on the phone...I've seen vending machines at a client office take Google Wallet payments.
As far as receipts, I try and avoid them when possible--they are just clutter that gets shredded when I get home (only time I keep the receipt is if it is something I might possibly need to return, which is nearly never).