You might have insurance that you're unaware of, such as a credit card that will replace stolen items purchased with the card for a period of time. Even if you discover that you have this insurance later, you may need the report to make a claim.
A police report provides a sworn statement that you can use as evidence that something was no longer in your possession after a certain time. This might be useful if you need to contest phone bills or credit card charges or if your property later turns up in connection with a crime.
It's possible that you'll get your items back, particularly if they can be described with specificity. Random cash, probably not, but a cell phone with serial number XYZ, it's at least possible. Even if it's unlikely for the police to go to any particular effort on your behalf, they'll have the information in their property database and may come across your property during other investigations. If you don't file a report, they won't know to contact you.
Reports of thefts also help the government gain information about the amount and location of crime, which could be used to help prevent theft in the future. Some governments are interested in attracting tourists and may take crime against visitors especially seriously because of the reputational damage it causes. Even if no specific action is taken on your report, it could be used to deploy more police to an area or investigate a broader pattern of criminal activity.
Some police departments in the United States (and based on a quick search, other countries as well) allow you to file simple police reports online for theft, which avoids most of the hassle of spending your vacation time talking to the police.