WHAT DO FORMER VOLUNTEERS SAY?
Clearly communicate that you are not there forever. For example, you can hang up balloons in the last 10 days if you work on a project with children. Then you puncture a balloon leak every day to indicate that you are about to leave. The explanation is then: "If the balloons are gone, then I am too."
If you have the luxury: take another month of 'vacation' in your home country then you allow yourself the time to see family and friends and take full days for what you would like to do at that time!
It is nice to give something to your project and/or host family when you say goodbye. Something that keeps them thinking about you doesn't have to be something big. A printed photo of all of you is fun! And let the people/children of your project, for example, write something in a book or draw what you can take home to think about them.