A performer dressed in costume prepares to participate in the Gay and Lesbian Mardi Gras parade in Sydney, Australia, March 5, 2016. The Sydney Mardi Gras parade began in 1978 as a march and commemoration of the 1969 Stonewall Riots of New York. It is an annual event promoting awareness of gay, lesbian, bisexual and transgender issues and themes. (Photo by David Gray/Reuters)

Julian, left, is photographed by his mother with friend Gianluca, right, under water at a public pool in Gelsenkirchen, Germany, on a hot Friday, July 3, 2015. Germany faces a heat wave with temperatures up to 38 degrees Celsius (100 degrees Fahrenheit) at the weekend. (Photo by Martin Meissner/AP Photo)

An aerial view of the lava erupting during volcanic eruption in September, in Bardarbunga, Iceland. Lava spews out from craters as molten rock flows into a river down the Bardarbunga volcano in Iceland. The dramatic pictures of the Holuhraun eruption were taken from an altitude of 50-500m on September 5-9 by Örvar Atli Þorgeirsson at twilight and with the stunning Aurora Borealis in the background. (Photo by Örvar Atli Þorgeirsson/Barcroft Media)

Kim Kardashian looks to have left her underwear at home as she heads out for an early dinner with boyfriend Kanye West in Miami on October 14, 2012. As Kim checked out her outfit in the reflection of her car, it became apparent that the reality star was not wearing any underwear as she showed off her see-through grey skirt. (Photo by Brett Kaffee/Thibault Monnier/PacificCoastNews.com)

Crowd members attempt to keep dry with umbrellas and ponchos prior to the 2012 Sydney Gay & Lesbian Mardi Gras Parade on March 3, 2012 in Sydney, Australia. (Photo by Brendon Thorne/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.

A patient buried in the hot sand looks out from under a shade that protects his face from the sun in Siwa, Egypt, August 12, 2015. In the searing heat of summer in western Egypt, at the hottest time of the day, sufferers of rheumatism, joint pain, infertility or impotence lie buried neck-deep in the sand of Siwa near Dakrour Mountain. Locals say taking a sand bath is a natural therapy with powers to cure many medical conditions. (Photo by Asmaa Waguih/Reuters)

Candice Swanepoel attends the Victoria's Secret Very s*xy Tour Stop in Dallas at Victoria's Secret Beauty at the NorthPark Mall on March 22, 2012 in Dallas, Texas. (Photo by Peter Larsen/ Getty Images for Victoria's Secret)