Tools to help stop losing things in public spaces

Hi,

I lost my purse today at the train, with cards, keys and plenty other things. It keeps happening and it needs to stop. I have a routine of always looking behind me, but mistakes keeps happening.

I looked around on this reddit for help, but it's mostly on routine change. I'm looking for useful physical tools that will make important things like phone, wallet, cards, etc. be close to impossible to lose. Currently considering a elastic string connected to my pants and purse, or get a wallet I can hang around my neck.

Anyone know other useful tools for this problem?