Take 50€ and put it somewhere safe, your suitcase, your travel documents, wherever. This way you'll have it just in case.
During the summer there is a huge line up of various ballet concerts available. Make sure you go and see one - where better to see Swan Lake than in St Petersburg?
I travelled on the European Contrasts tour in May 2006 with my boyfriend. We had 5 couples on our tour. We all had a great time and did not have any hassles being that we were couples.