Take 50€ and put it somewhere safe, your suitcase, your travel documents, wherever. This way you'll have it just in case.
My advice would be to do as many excursions as you can. They are a great way to get to know your group, and they are always good fun.
I dont think anyone has ever said they didnt enjoy George's boat! Its by far the best optional on tour! The water is amazing and George is quite the entertainer ;)