It might be something you don't want to do when you are on holiday, but it is also a very essential part of managing your finances on the trip. Bring back bills of every payment you make, perhaps at the mall or tickets at an attraction. At the end of the day note them all down and calculate exactly how much you have to remain. Plan out the next day accordingly. To make things more organised you can divide your expenses into categories like hygiene, accommodation, transport, tours and food & drinks.