First you should develop a routine with your stuff and remember less is more! So if you can ditch the bag!
Wallets in your front pocket are hard to get for the opportunist bump pickpocket.
Purse or sling bags should have a flap and a zipper.
Clip your wallet in your bag then zip it up, fold the flap and clip it shut. Keep your bag in front of you when on the train or in busy markets. Once the wallet is out and in the hands of a thief it could be shuffled around you like a shell game or on the other side of the subway doors after they have closed.
When at a café or restaurant, I try to avoid the table closest to the door or edge of the square. I will use a carabiner and clip my bag to the chair I’m sitting in (twist lock carabiner). I also try to sit across from my travel companion (I got your back you got mine).
In a lot of thefts there is a distraction just prior. It could be someone dropping change, a couple arguing, a vender holding something in front of you or someone trying to get your attention from across the street. (Even call out your name from eavesdropping earlier)
The idea here is make it difficult so they look for an easier target!
(Don’t be the low hanging fruit.)
Keep traveling and be safe out there!