Louise Michel wrote a bit about the difference between property of good (the fact of owning) and possession, that is mostly linked to the fact that you are using something or that it's important to you (and no one claims it his/her own). Which remains very meaningful to me.
I think that stealing possessions from poor people is an act of great social violence. In fact, that's what bailiffs and cops are doing in a seizure, or when they steal yours stuff during a "search"/perquisition.
And this is not only violent because it's the state. Mostly it's an act of violence and power by which the powerful distinguish themselves.
What makes all the difference with expropriation is that its not a question of personnal stuff or possessions but of property among things or places you don't need only for yourself and use to exploit ressources or the force of other people to make business and capital.
That is what makes all the difference between property and personnal (or even collective) possession to me.
The purpose of what Louise Michel said is that basically the only kind of real anarchist expropriation or autoreductions (extorsion, robbery or theft in law) is "possession taking". You don't take something only for yourself, or at least, you don't steal it because you think it's your "due", or "personnal good" or your "property" but so as to break it's property or commodity aspect.
Which is to say that you are not really "stealing" something from someone (as the commodity produced by someone which had been stolen his work and the fruit of his work don't really belong to anyone), but only using the "usufruct" of it, to use a legal word. :-D
To me stealing something from someone is to "deprive" someone from something she or he actually possess because she or he made it, needs it, and/or use it. And to be more specific, by deprive, I mean taking something by force to make it your own at the expense of someone else. That's my anarchist definition of "theft" that have nothing in common with the law.
But that doesn't make it "okay" to take something from someone just because you considere this person didn't really "need it". I think that in an "more anarchistic world", or in non dominant social relationships, you wouldn't force someone to give you something you don't really need. And you won't also be very attached to objects you don't need or really matters to you.
That's why this question seems always open to me as we live in a world where the relation to goods, property and possession are completly confused in fetichist and alienated relationships to objects, places and commodities.
I have no idea what we should do in a "idealistic society" against theft, but I think we shouldn't blame people more than they affected us with such actions until they are often pushed to do so by ignorance, or selfish "instinct" of survival that this society teach.
So, to answer your question, I think that "theft" isn't a problem if we are talking about the goods of the bourgeoisie, or commodities because it's not really "theft". But I also think we shouldn't blame people too much when they steal something in an interpersonnal context.
And so, the main thing you can do in general against people stealing each other is to destroy a society that promoted theft of force, life and fruits of labor as a normal way to operate. Aka Capitalism. And by the way tell anyone around you not to accumulate goods, capital and things they don't need and that if they need to steal things to survive, they should do it against rich people or the industrial and luxury shops of distribution of commodities rather than stealing each other between poor or normal/modest people.
Kropotkine uses a expression of an anarchist economic concept that I couldn't translate. It's something like "taking in the lot".
By the way, I think we may all drink affordable herbal tea.
Because proper tea is theft.
