In this handout image provided by the Police of Swiss canton Valais the wreckage of a bus is seen after it crashed inside a motorway tunnel on March 13, 2012 in Sierre, Switzerland. 28 people, including 22 children, returning from a skiing holiday died in this bus accident. (Photo by Police Cantonale Valaisanne via Getty Images)

Shanghai-based artist Hong Yi, also known as Red, used 750 pair of socks to create a rather unusual sock portrait of famous Chinese film director Zhang Yimou. Yi, which is famous for her Coffee Stain Portrait, spent over three weeks on the project and used black, white and grey socks. (Photo by Ohiseered.com)

The 8th annual Miss International Queen beauty pageant was held in Pattaya in Thailand. The twenty-one contestants from fifteen countries were all born male, so the Miss International Queen 2012 pageant is not an average beauty pageant.

Photo: Panvilas Mongkol, a contestant from Thailand, waits for the start of the final night of Miss International Queen 2012 transgender/transsexual beauty pageant in Pattaya November 2, 2012. Some 21 contestants from 15 countries, all of them born male, compete in the week-long event for the crown of Miss International Queen 2012. (Photo by Damir Sagolj/Reuters)

People take photographs of waves crashing against the harbour wall on January 3, 2012 in Porthcawl, Wales. (Photo by Matt Cardy/Getty Images)

Fireplace for children, Trondheim, Norway, by Haugen/Zohar. The children of Trondheim come to sit around the fire and tell stories in this whimsical cone hut, made with materials recycled from a construction site. (Photo by Jason Havneraas/The Guardian)

Radio City Music Hall Rockettes perform after days of rehearsal and routine polished to perfection at the Radio City Music Hall in New York City on July 26, 1949. (Photo by Ivan Dmitri/Getty Images)

Sеxy brunet striptease dancer dancing lap dance in front of man. (Photo by Blue SkyImages/Getty Images)

Everyone wants to get something for nothing - whether it's a lucky upgrade that means you can turn left when you get on a plane instead or heading off into the economy seats, or even getting a few extra features thrown in for free when you buy a new car.

As some of the sharpest businesses around, no-one understands this quite as well as casinos and that's why they all have a system that they call comps. It's short for "complimentary offers" and these are special treats specially designed to reward you for your loyalty to the casino in question. They're basically bonuses.