The retired bishop of Rupertsland, Walter Jones, used to fly a lot between Toronto and Winnipeg. On his homeward trips he'd make a point of quietly saying to the desk staff that if they needed someone to relinquish their seat he'd be happy to take the next flight. Over the years he collected thousands of dollars worth of flight vouchers and occasional cash which he used sometimes for church business and sometimes for family travel.
Having learned that from him, I've done it myself a few times ... proactively volunteered to relinquish my seat. I never got cash but I did score some juicy flight coupons and once, a free night in a luxurious Toronto hotel.
