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.

Opossums on their mothers back at a game reserve in Central Minnesota, USA, on September 2, 2013. (Photo by Caters News Agency)

Children guarded by Hungarian police play on the ground after being detained along with other migrants who illegally crossed from Serbia to Hungary near the village of Asotthalom, Hungary, September 16, 2015. (Photo by Dado Ruvic/Reuters)

Where Children Sleep – stories of diverse children around the world, told through portraits and pictures of their bedrooms by James Mollison. This is a selection from the 56 diptychs in the book (Chris Boot November 2010). The book is written and presented for an audience of 9-13 year olds‘ intended to interest and engage children in the details of the lives of other children around the world, and the social issues affecting them, while also being a serious photographic essay for an adult audience.

Kerry Katona carries Peter McDonagh's flag before he faces Peter Krame during their Super welterweight bout at the Bolton Whites Hotel, Bolton, United Kingdom on May 12, 2018. (Photo by Lee Smith/Action Images via Reuters)

English reality television personality and country music singer Megan Elizabeth McKenna is seen at Soho House on May 24, 2018 in London, United Kingdom. (Photo by Splash News and Pictures)

Chloe Khan dressed as Princess Jasmine from Aladdin seen on October 31, 2017 in London, England. (Photo by iCelebTV)

People are seen on a street in Havana December 17, 2014. Stunned Cubans celebrated an apparent end to decades of conflict with the United States on Wednesday after both governments said they would restore diplomatic relations cut off in 1961. Many said they expected a restoration of ties would lead to the end of a U.S. economic embargo against Cuba, which is vilified daily in the official media and which Cubans accept as a key cause of widespread poverty on the island. (Photo by Reuters/Stringer)