Question about traveling and avoiding pickpocketers?

I am 17 and I am going to London and France this summer as an exchange girl. I am going to be traveling with an 18 year old French girl but I am extremely worried about pickpocketers. I am looking into getting a neck pouch or money belt to keep my passport and some money in, but I was wondering what I do with the rest of my stuff? Like where do I keep my digital camera and my phone since those will obviously not fit in my pouch. I am nervous to carry a bag with them because I know those can easily be slashed open by a pickpocketer. Any tips? Thanks so much! :)