When you are on holiday although it may seem alien to you it is important that in order to show your appreciation of the service in various restaurants, bars and cafes that you leave a tip for the staff. But of course the reason why most people tend not to leave a tip especially when a broad is that they don't know if one is required or not.
However, in all honesty when ever on holiday it is a good idea to leave the staff who have served you a tip that isn't any more than 10% of the total bill. So therefore if your bill has come to say 40 Euros then a tip of between 2 and 4 Euros would suffice. However, for small bills then you can leave just 1 Euro for them.
So of course before you do go on holiday it is a good idea to include in the money you are putting aside for paying for food etc that you include a sum to cover tipping. If you don't then you may find yourself in a situation where you end up having to get more money out or not buy a present for a loved one back home.