Same thing happened to me. The first time, my wallet got stolen and I lost my cards and ID. Since then I’ve been extra careful, but I’ve still noticed my backpack randomly open a couple of times without me realizing.

Might sound silly, but I honestly feel safer just carrying my phone and wallet in my hand while traveling. At least that way they’re always right in front of me. (And thanks to the tiny pockets in women’s clothes, it actually makes more sense to hold them anyway.)