Best I ever did was back in high school. It was a student group going to Germany, and the travel agent botched the reservations, and they didn't have room for all of us from ORD to Dusseldorf.

AA offers us $800 each if they reroute our group through Manchester, UK. (We'd paid about $750 each for a 3 week homestay trip with some bus excursions) So the group says "You betcha" and we end up in Manchester, where somehow either AA or BA managed to lose our reservation information again, and about 2/3 of the group ended up in first class between Manchester and Dusseldorf because that was where there was room on the next flight. (Alas, not me.)

So between my chaperone father (who went free because the group was big enough to get him that perk) and I, we ended up with $1600 on my $750 vacation.

Our family of four spent the next Spring Break on St. Croix because of the vouchers.