After spending months in Europe I never had anything stolen by a pickpocket-not that it is impossible, but I have been thoughtful and lucky.
So, your money belt will have your passport, back up cards, and any large amounts of cash you are carrying. Your wallet should therefor only have some cash for a day or two (100 Euro?) and one card for any large or automated machine purchase. Your bag will also have your phone, a camera, and sundry items you may need, as mentioned above. What are you worried about exactly? Your money belt is secure, your daily cash isn't much, and you know who to call if your card gets taken. And your phone is just a phone, secure it but it is Just A Phone. Don't get me wrong, I would be extremely upset if I lost my phone especially since it has my email (with ticket info) and other info, but it's just a hiccup and the trip would go on.
Now, think like a pickpocket. First of all, pickpockets are the main problem, not purse snatchers, so you will not lose your tickets, maps, sundries. If he or she has to unclip, lift a flap, unzip, and reach down up to his elbow, then most likely whatever is in the bottom of that bag won't get taken. If you don't need your phone, bury it in your bag under the maps and books, and put your wallet down there with it. Keep a few euro coins in one of the zipper pockets for bathrooms or quick drinks. Pull your bag in front of you when you are in crowded tourist areas, set it on you lap on public transportation, put it between your feet at a restaurant (a pickpocket won't crawl under the table), and just be conscious of what is going on around you. Do a bag check with your travel companions, making sure all zippers are zipped and everyone's bags are closed when you leave a place. You will be fine, and nothing irreplaceable is in that bag, and if those few coins are taken, well you have the best story to post on the forum.
Remember, there are tons of helpful, honest Europeans too. Someone above mentioned a wallet being taken, but also BEING RETURNED by another person who saw what happened. A small bag fell out of my backpack, and an Italian couple picked it up and came after me to return it. Keep an eye out for those people, too.
I know you will have a fantastic trip! Bon Voyage!