Bring summer clothes - cotton, thin viscose fabrics, and silk are most comfortable to wear; linen is too heavy. Cambodia is, like Thailand, a conservative country and visitors in skimpy attire are frowned upon. Your clothes do not have to be elegant but they should be clean and cover everything from the shoulders to the knees. This also prevents sunburn, which is easily caught under the hot tropical sun. A hat or cap are highly recommended to prevent heat stroke.  Reasonable, strong walking shoes are recommended if you want to visit and explore temples at Angkor.