Party-goers partake in a festival better known as Holi One, during International Workers Day in Johannesburg, South Africa, 01 May 2015. The colour festival promotes togetherness as well as colourness in everday life. May Day is observed worldwide every year on 01 May. (Photo by Kevin Sutherland/EPA)

Taronga Zoo's elephant baby, as yet unnamed, is seen at Taronga Zoo on March 12, 2010 in Sydney, Australia. The Asian Elephant calf has continued to make progress following a protracted labour that spanned six days. The calf was originally believed to have died in the womb during labour but surprised veterinarians and zoo staff with an unexpected delivery early Wednesday morning. (Photo by Bobby-Jo Vial/Taronga Zoo via Getty Images)

Finding just the right spot above the clouds at Camp 1 on Ama Dablam, Danuru Sherpa uses his iPhone to catch up with friends and family. Even at 18,500 feet (5,654 meters), climbers here can check their email and other dispatches from the world below. (Photo by Aaron Huey/National Geographic)

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.

Whitney Houston's body arrives at Whigham Funeral Home on February 13, 2012 in Newark, New Jersey. (Photo by Dave Kotinsky/Getty Images)

In this June 29, 2015 photo, forlorn buildings are seen at Hashima Island, commonly known as Gunkanjima, which means “Battleship Island”, off Nagasaki, Nagasaki Prefecture, southern Japan. The island is one of 23 old industrial facilities seeking UNESCO's recognition as world heritage “Sites of Japan's Meiji Industrial Revolution” meant to illustrate Japan's rapid transformation from a feudal farming society into an industrial power at the end of the 19th century. UNESCO's World Heritage Committee is expected to approve the proposal during a meeting being held in Bonn, Germany, through July 9. (Photo by Eugene Hoshiko/AP Photo)

A doll, placed by stranded Iranian migrant protesters, hangs from barbed wire in front of Madedonian police at the Greek-Macedonian border near to the Greek village of Idomeni November 29, 2015. The protesters were demonstrating against what they say is the closure of the border for Iranian migrants. According to the demonstrators, the hanging toys and dolls represent the outcome of being unable to return, if they are sent back to Iran. (Photo by Yannis Behrakis/Reuters)

The Blue Lagoon geothermal spa is one of the most visited attractions in Iceland. The spa is located in a lava field in Grindavík on the Reykjanes Peninsula, southwestern Iceland. Bláa lónið is situated approximately 13 km (8 miles) from the Keflavík International Airport and 39 km (24 miles) from the capital city of Reykjavík. That is roughly a 20 minute drive from the airport and a 40 minute drive from Reykjavík.