Electronic Receipts for Traditional Purchases
Purchases made in person in stores have a disadvantage for customers in that there is no electronic record of the purchase available for the customer, only a paper receipt. Since receipts are often needed for returns, proof-of-purchase, rebates, etc., there is motivation to mimic internet sales with electronic receipts. If the customer was willing to give their email address to the store clerk, these could be sent by email (along with advertising). If the customer wanted to remain anonymous, but still wanted a receipt, there could be a swip-able card that could record the purchase information (and advertisements).
Reward: Recognition for development of the idea.