I always keep the pouch in front of me, never in the back.
I found what works better is just a little travel purse that you have over your shoulder with it in front of you. I've learned this from living in NYC. It also keeps your hands free and keeps the purse in front of you. I would never put a purse on my shoulder.
You are better off putting your credit card and money in your front pants/shirt pocket and just keep your cruise card and glasses etc in the pack.
The key is to be always be aware of what is going on around you and you should be okay.