I'm going to move a stranger's bag on a train
Why do you want to move his bag?
I've been stepping on his foot accidentally and I want him to pay attention to that.
Though their belongings may be in the way, you should communicate with them and get their consent before touching their things. They may think you are stealing from them if you move their belongings without consent.
I will move his shit anyway
If you move their stuff without asking you may really anger them. You should just kindly tell them to put it somewhere else.