International tourists are required to buy and keep their tickets safe during their whole trip to the Angkor Archaeological Site. If you lose your ticket, you won't be allowed to enter the Angkor park.
Moreover, there is a strict dress code in operation at all temples located in Siem Reap. Both males and females should wear clothes properly that cover your shoulders and upper leg. If you don't conform to the dress code you won't be able to purchase a ticket and you won't be allowed to enter the site.