They give flight vouchers, but they often have other direct expenses like hotel accommodations and food.

The last time I was bumped it was ~$600 airline voucher, transportation to/from a ski resort (a perk of being bumped in the mountains!), a room for the night and a good meal voucher to cover dinner and breakfast the next day. Plus they still flew me out the next day and took care of rebooking the connection on another airline. I don't know exactly how much it cost them, but I made out like a bandit.

I can better that. In the early 90s I (12) and a schoolmate (17) were flying vancouver-toronto-london with BA. I as an unaccompanied minor, him no so. The toronto-london flight was delayed overnight due to mechanical issues. They probably wouldn't have helped my friend so much but when I mentioned there was an older student on the flight from the same school they tracked him down. We got two hotel rooms and, this sounds strange but true, a stewardess. She took us to visit the University of Toronto, to which my friend was applying, and then the CN tower before our flight the following night.